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 $211.85   12.414%   $238.1491   $238.15   $238.15   $238.10  
  Purchase #2 $228.35   3.465%   $236.2623   $236.26   $236.25   $236.30  
  Purchase #3 $49.94   12.626%   $56.2454   $56.25   $56.25   $56.20  
  Purchase #4 $158.57   6.162%   $168.3411   $168.34   $168.35   $168.30  
  Purchase #5 $111.38   6.533%   $118.6565   $118.66   $118.65   $118.70  
  Purchase #6 $24.55   6.823%   $26.225   $26.23   $26.25   $26.20  
  Purchase #7 $90.91   3.698%   $94.2719   $94.27   $94.25   $94.30  
  7 purchase totals = $875.55       $938.1513   $938.16   $938.15   $938.10