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 $204.48   12.188%   $229.402   $229.40   $229.40   $229.40  
  Purchase #2 $99.47   10.474%   $109.8885   $109.89   $109.90   $109.90  
  Purchase #3 $73.79   3.752%   $76.5586   $76.56   $76.55   $76.60  
  Purchase #4 $68.35   3.807%   $70.9521   $70.95   $70.95   $71.00  
  Purchase #5 $186.31   3.604%   $193.0246   $193.02   $193.00   $193.00  
  Purchase #6 $192.93   5.434%   $203.4138   $203.41   $203.40   $203.40  
  Purchase #7 $59.58   8.816%   $64.8326   $64.83   $64.85   $64.80  
  7 purchase totals = $884.91       $948.0722   $948.06   $948.05   $948.10