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 $194.79   10.488%   $215.2196   $215.22   $215.20   $215.20  
  Purchase #2 $242.79   13.289%   $275.0544   $275.05   $275.05   $275.10  
  Purchase #3 $41.73   9.781%   $45.8116   $45.81   $45.80   $45.80  
  Purchase #4 $64.34   13.156%   $72.8046   $72.80   $72.80   $72.80  
  Purchase #5 $79.76   7.217%   $85.5163   $85.52   $85.50   $85.50  
  Purchase #6 $222.80   4.229%   $232.2222   $232.22   $232.20   $232.20  
  Purchase #7 $177.60   8.694%   $193.0405   $193.04   $193.05   $193.00  
  7 purchase totals = $1,023.81       $1,119.6692   $1,119.66   $1,119.60   $1,119.60