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 $64.49   4.847%   $67.6158   $67.62   $67.60   $67.60  
  Purchase #2 $239.66   5.601%   $253.0834   $253.08   $253.10   $253.10  
  Purchase #3 $246.32   5.505%   $259.8799   $259.88   $259.90   $259.90  
  Purchase #4 $118.91   8.485%   $128.9995   $129.00   $129.00   $129.00  
  Purchase #5 $246.58   10.858%   $273.3537   $273.35   $273.35   $273.40  
  Purchase #6 $58.28   10.441%   $64.365   $64.37   $64.35   $64.40  
  Purchase #7 $169.94   11.583%   $189.6242   $189.62   $189.60   $189.60  
  7 purchase totals = $1,144.18       $1,236.9215   $1,236.92   $1,236.90   $1,237.00