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 $6.58   8.410%   $7.1334   $7.13   $7.15   $7.10  
  Purchase #2 $21.96   8.620%   $23.853   $23.85   $23.85   $23.90  
  Purchase #3 $158.71   12.310%   $178.2472   $178.25   $178.25   $178.20  
  Purchase #4 $107.79   7.762%   $116.1567   $116.16   $116.15   $116.20  
  Purchase #5 $138.49   3.581%   $143.4493   $143.45   $143.45   $143.40  
  Purchase #6 $215.38   8.870%   $234.4842   $234.48   $234.50   $234.50  
  Purchase #7 $197.94   13.527%   $224.7153   $224.72   $224.70   $224.70  
  7 purchase totals = $846.85       $928.0391   $928.04   $928.05   $928.00