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 $61.59   10.743%   $68.2066   $68.21   $68.20   $68.20  
  Purchase #2 $109.39   12.863%   $123.4608   $123.46   $123.45   $123.50  
  Purchase #3 $5.97   8.156%   $6.4569   $6.46   $6.45   $6.50  
  Purchase #4 $246.37   6.525%   $262.4456   $262.45   $262.45   $262.40  
  Purchase #5 $204.90   9.841%   $225.0642   $225.06   $225.05   $225.10  
  Purchase #6 $112.62   12.615%   $126.827   $126.83   $126.85   $126.80  
  Purchase #7 $66.41   13.518%   $75.3873   $75.39   $75.40   $75.40  
  7 purchase totals = $807.25       $887.8484   $887.86   $887.85   $887.90