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 $65.66   12.206%   $73.6745   $73.67   $73.65   $73.70  
  Purchase #2 $212.61   13.567%   $241.4548   $241.45   $241.45   $241.50  
  Purchase #3 $48.88   3.854%   $50.7638   $50.76   $50.75   $50.80  
  Purchase #4 $82.34   9.516%   $90.1755   $90.18   $90.20   $90.20  
  Purchase #5 $49.65   13.712%   $56.458   $56.46   $56.45   $56.50  
  Purchase #6 $59.43   8.682%   $64.5897   $64.59   $64.60   $64.60  
  Purchase #7 $224.87   4.532%   $235.0611   $235.06   $235.05   $235.10  
  7 purchase totals = $743.44       $812.1774   $812.17   $812.15   $812.40