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 $86.58   13.393%   $98.1757   $98.18   $98.20   $98.20  
  Purchase #2 $112.64   11.630%   $125.74   $125.74   $125.75   $125.70  
  Purchase #3 $87.46   7.201%   $93.758   $93.76   $93.75   $93.80  
  Purchase #4 $178.66   13.175%   $202.1985   $202.20   $202.20   $202.20  
  Purchase #5 $153.56   13.320%   $174.0142   $174.01   $174.00   $174.00  
  Purchase #6 $43.49   5.220%   $45.7602   $45.76   $45.75   $45.80  
  Purchase #7 $194.61   9.357%   $212.8197   $212.82   $212.80   $212.80  
  7 purchase totals = $857.00       $952.4663   $952.47   $952.45   $952.50