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 $63.78   3.492%   $66.0072   $66.01   $66.00   $66.00  
  Purchase #2 $25.63   6.626%   $27.3282   $27.33   $27.35   $27.30  
  Purchase #3 $118.69   5.507%   $125.2263   $125.23   $125.25   $125.20  
  Purchase #4 $65.43   6.144%   $69.45   $69.45   $69.45   $69.50  
  Purchase #5 $130.53   3.582%   $135.2056   $135.21   $135.20   $135.20  
  Purchase #6 $33.63   3.319%   $34.7462   $34.75   $34.75   $34.70  
  Purchase #7 $222.26   8.668%   $241.5255   $241.53   $241.55   $241.50  
  7 purchase totals = $659.95       $699.4890   $699.51   $699.55   $699.40