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 $106.91   5.307%   $112.5837   $112.58   $112.60   $112.60  
  Purchase #2 $20.52   12.606%   $23.1068   $23.11   $23.10   $23.10  
  Purchase #3 $101.80   5.340%   $107.2361   $107.24   $107.25   $107.20  
  Purchase #4 $193.85   5.616%   $204.7366   $204.74   $204.75   $204.70  
  Purchase #5 $241.42   11.142%   $268.319   $268.32   $268.30   $268.30  
  Purchase #6 $105.56   4.666%   $110.4854   $110.49   $110.50   $110.50  
  Purchase #7 $86.97   13.216%   $98.464   $98.46   $98.45   $98.50  
  7 purchase totals = $857.03       $924.9316   $924.94   $924.95   $924.90