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 $241.72   3.859%   $251.048   $251.05   $251.05   $251.00  
  Purchase #2 $148.74   10.396%   $164.203   $164.20   $164.20   $164.20  
  Purchase #3 $57.90   12.665%   $65.233   $65.23   $65.25   $65.20  
  Purchase #4 $228.84   5.487%   $241.3965   $241.40   $241.40   $241.40  
  Purchase #5 $109.80   11.203%   $122.1009   $122.10   $122.10   $122.10  
  Purchase #6 $217.84   3.358%   $225.1551   $225.16   $225.15   $225.20  
  Purchase #7 $240.50   5.773%   $254.3841   $254.38   $254.40   $254.40  
  7 purchase totals = $1,245.34       $1,323.5206   $1,323.52   $1,323.55   $1,323.50