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 $41.50   11.825%   $46.4074   $46.41   $46.40   $46.40  
  Purchase #2 $239.87   5.483%   $253.0221   $253.02   $253.00   $253.00  
  Purchase #3 $232.44   7.868%   $250.7284   $250.73   $250.75   $250.70  
  Purchase #4 $67.57   3.351%   $69.8343   $69.83   $69.85   $69.80  
  Purchase #5 $50.81   4.421%   $53.0563   $53.06   $53.05   $53.10  
  Purchase #6 $23.51   8.708%   $25.5573   $25.56   $25.55   $25.60  
  Purchase #7 $165.47   7.768%   $178.3237   $178.32   $178.30   $178.30  
  7 purchase totals = $821.17       $876.9295   $876.93   $876.90   $876.90