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 $45.91   4.216%   $47.8456   $47.85   $47.85   $47.80  
  Purchase #2 $60.63   11.151%   $67.3909   $67.39   $67.40   $67.40  
  Purchase #3 $11.62   5.193%   $12.2234   $12.22   $12.20   $12.20  
  Purchase #4 $139.56   9.201%   $152.4009   $152.40   $152.40   $152.40  
  Purchase #5 $98.81   4.579%   $103.3345   $103.33   $103.35   $103.30  
  Purchase #6 $183.59   11.648%   $204.9746   $204.97   $204.95   $205.00  
  Purchase #7 $201.97   4.331%   $210.7173   $210.72   $210.70   $210.70  
  7 purchase totals = $742.09       $798.8872   $798.88   $798.85   $798.80