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 $207.38   12.134%   $232.5435   $232.54   $232.55   $232.50  
  Purchase #2 $136.73   12.602%   $153.9607   $153.96   $153.95   $154.00  
  Purchase #3 $147.33   7.412%   $158.2501   $158.25   $158.25   $158.30  
  Purchase #4 $235.72   3.596%   $244.1965   $244.20   $244.20   $244.20  
  Purchase #5 $147.90   8.306%   $160.1846   $160.18   $160.20   $160.20  
  Purchase #6 $207.44   5.661%   $219.1832   $219.18   $219.20   $219.20  
  Purchase #7 $245.84   7.751%   $264.8951   $264.90   $264.90   $264.90  
  7 purchase totals = $1,328.34       $1,433.2137   $1,433.21   $1,433.25   $1,433.30