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 $233.96   13.826%   $266.3073   $266.31   $266.30   $266.30  
  Purchase #2 $199.68   3.837%   $207.3417   $207.34   $207.35   $207.30  
  Purchase #3 $129.72   11.694%   $144.8895   $144.89   $144.90   $144.90  
  Purchase #4 $31.67   12.489%   $35.6253   $35.63   $35.65   $35.60  
  Purchase #5 $6.93   4.734%   $7.2581   $7.26   $7.25   $7.30  
  Purchase #6 $133.44   13.484%   $151.433   $151.43   $151.45   $151.40  
  Purchase #7 $238.53   7.273%   $255.8783   $255.88   $255.90   $255.90  
  7 purchase totals = $973.93       $1,068.7332   $1,068.74   $1,068.80   $1,068.70