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 $108.55   5.218%   $114.2141   $114.21   $114.20   $114.20  
  Purchase #2 $244.75   11.140%   $272.0152   $272.02   $272.00   $272.00  
  Purchase #3 $65.62   12.142%   $73.5876   $73.59   $73.60   $73.60  
  Purchase #4 $13.73   3.454%   $14.2042   $14.20   $14.20   $14.20  
  Purchase #5 $40.87   4.395%   $42.6662   $42.67   $42.65   $42.70  
  Purchase #6 $101.52   4.758%   $106.3503   $106.35   $106.35   $106.40  
  Purchase #7 $165.87   3.252%   $171.2641   $171.26   $171.25   $171.30  
  7 purchase totals = $740.91       $794.3017   $794.30   $794.25   $794.40