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 $42.30   10.122%   $46.5816   $46.58   $46.60   $46.60  
  Purchase #2 $10.38   4.420%   $10.8388   $10.84   $10.85   $10.80  
  Purchase #3 $57.77   5.599%   $61.0045   $61.00   $61.00   $61.00  
  Purchase #4 $164.46   5.576%   $173.6303   $173.63   $173.65   $173.60  
  Purchase #5 $199.76   12.652%   $225.0336   $225.03   $225.05   $225.00  
  Purchase #6 $244.37   5.727%   $258.3651   $258.37   $258.35   $258.40  
  Purchase #7 $218.39   8.121%   $236.1255   $236.13   $236.15   $236.10  
  7 purchase totals = $937.43       $1,011.5794   $1,011.58   $1,011.65   $1,011.50