Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.26   10.351%   $225.403   $225.40   $225.40   $225.40  
  Purchase #2 $119.93   3.680%   $124.3434   $124.34   $124.35   $124.30  
  Purchase #3 $245.42   10.307%   $270.7154   $270.72   $270.70   $270.70  
  Purchase #4 $129.28   9.544%   $141.6185   $141.62   $141.60   $141.60  
  Purchase #5 $217.26   13.502%   $246.5944   $246.59   $246.60   $246.60  
  Purchase #6 $106.55   9.194%   $116.3462   $116.35   $116.35   $116.30  
  Purchase #7 $125.89   13.475%   $142.8537   $142.85   $142.85   $142.90  
  7 purchase totals = $1,148.59       $1,267.8746   $1,267.87   $1,267.85   $1,267.80