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 $214.93   6.624%   $229.167   $229.17   $229.15   $229.20  
  Purchase #2 $225.81   13.244%   $255.7163   $255.72   $255.70   $255.70  
  Purchase #3 $235.43   5.120%   $247.484   $247.48   $247.50   $247.50  
  Purchase #4 $102.87   12.860%   $116.0991   $116.10   $116.10   $116.10  
  Purchase #5 $216.72   5.264%   $228.1281   $228.13   $228.15   $228.10  
  Purchase #6 $44.77   6.829%   $47.8273   $47.83   $47.85   $47.80  
  Purchase #7 $91.68   4.450%   $95.7598   $95.76   $95.75   $95.80  
  7 purchase totals = $1,132.21       $1,220.1816   $1,220.19   $1,220.20   $1,220.20