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 $45.59   5.590%   $48.1385   $48.14   $48.15   $48.10  
  Purchase #2 $155.74   5.403%   $164.1546   $164.15   $164.15   $164.20  
  Purchase #3 $129.55   3.369%   $133.9145   $133.91   $133.90   $133.90  
  Purchase #4 $243.37   5.790%   $257.4611   $257.46   $257.45   $257.50  
  Purchase #5 $219.29   5.495%   $231.34   $231.34   $231.35   $231.30  
  Purchase #6 $94.51   10.391%   $104.3305   $104.33   $104.35   $104.30  
  Purchase #7 $49.25   7.617%   $53.0014   $53.00   $53.00   $53.00  
  7 purchase totals = $937.30       $992.3406   $992.33   $992.35   $992.30