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 $244.73   12.592%   $275.5464   $275.55   $275.55   $275.50  
  Purchase #2 $100.66   10.239%   $110.9666   $110.97   $110.95   $111.00  
  Purchase #3 $173.39   3.345%   $179.1899   $179.19   $179.20   $179.20  
  Purchase #4 $232.64   6.387%   $247.4987   $247.50   $247.50   $247.50  
  Purchase #5 $165.48   13.792%   $188.303   $188.30   $188.30   $188.30  
  Purchase #6 $194.85   5.241%   $205.0621   $205.06   $205.05   $205.10  
  Purchase #7 $158.82   6.680%   $169.4292   $169.43   $169.45   $169.40  
  7 purchase totals = $1,270.57       $1,375.9959   $1,376.00   $1,376.00   $1,376.00