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 $177.67   7.563%   $191.1072   $191.11   $191.10   $191.10  
  Purchase #2 $225.48   12.281%   $253.1712   $253.17   $253.15   $253.20  
  Purchase #3 $83.86   11.452%   $93.4636   $93.46   $93.45   $93.50  
  Purchase #4 $16.42   5.533%   $17.3285   $17.33   $17.35   $17.30  
  Purchase #5 $44.95   8.268%   $48.6665   $48.67   $48.65   $48.70  
  Purchase #6 $122.53   3.580%   $126.9166   $126.92   $126.90   $126.90  
  Purchase #7 $223.70   3.617%   $231.7912   $231.79   $231.80   $231.80  
  7 purchase totals = $894.61       $962.4448   $962.45   $962.40   $962.50