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 $208.75   12.350%   $234.5306   $234.53   $234.55   $234.50  
  Purchase #2 $24.35   9.328%   $26.6214   $26.62   $26.60   $26.60  
  Purchase #3 $208.43   8.102%   $225.317   $225.32   $225.30   $225.30  
  Purchase #4 $152.74   3.495%   $158.0783   $158.08   $158.10   $158.10  
  Purchase #5 $118.31   8.371%   $128.2137   $128.21   $128.20   $128.20  
  Purchase #6 $138.29   10.494%   $152.8022   $152.80   $152.80   $152.80  
  Purchase #7 $48.78   5.853%   $51.6351   $51.64   $51.65   $51.60  
  7 purchase totals = $899.65       $977.1983   $977.20   $977.20   $977.10