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 $137.73   3.523%   $142.5822   $142.58   $142.60   $142.60  
  Purchase #2 $46.75   11.170%   $51.972   $51.97   $51.95   $52.00  
  Purchase #3 $8.68   12.157%   $9.7352   $9.74   $9.75   $9.70  
  Purchase #4 $224.37   3.738%   $232.757   $232.76   $232.75   $232.80  
  Purchase #5 $205.81   12.682%   $231.9108   $231.91   $231.90   $231.90  
  Purchase #6 $203.62   12.662%   $229.4024   $229.40   $229.40   $229.40  
  Purchase #7 $141.38   4.716%   $148.0475   $148.05   $148.05   $148.00  
  7 purchase totals = $968.34       $1,046.4071   $1,046.41   $1,046.40   $1,046.40