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 $24.30   11.181%   $27.017   $27.02   $27.00   $27.00  
  Purchase #2 $80.94   4.187%   $84.329   $84.33   $84.35   $84.30  
  Purchase #3 $89.94   7.551%   $96.7314   $96.73   $96.75   $96.70  
  Purchase #4 $167.96   13.409%   $190.4818   $190.48   $190.50   $190.50  
  Purchase #5 $194.42   11.589%   $216.9513   $216.95   $216.95   $217.00  
  Purchase #6 $222.68   9.793%   $244.4871   $244.49   $244.50   $244.50  
  Purchase #7 $247.62   3.536%   $256.3758   $256.38   $256.40   $256.40  
  7 purchase totals = $1,027.86       $1,116.3734   $1,116.38   $1,116.45   $1,116.40