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 $134.92   13.545%   $153.1949   $153.19   $153.20   $153.20  
  Purchase #2 $61.63   7.124%   $66.0205   $66.02   $66.00   $66.00  
  Purchase #3 $109.92   9.783%   $120.6735   $120.67   $120.65   $120.70  
  Purchase #4 $173.30   10.341%   $191.221   $191.22   $191.20   $191.20  
  Purchase #5 $50.92   7.145%   $54.5582   $54.56   $54.55   $54.60  
  Purchase #6 $126.33   10.278%   $139.3142   $139.31   $139.30   $139.30  
  Purchase #7 $31.81   8.211%   $34.4219   $34.42   $34.40   $34.40  
  7 purchase totals = $688.83       $759.4042   $759.39   $759.30   $759.40