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 $131.55   11.767%   $147.0295   $147.03   $147.05   $147.00  
  Purchase #2 $102.25   10.669%   $113.1591   $113.16   $113.15   $113.20  
  Purchase #3 $170.49   13.662%   $193.7823   $193.78   $193.80   $193.80  
  Purchase #4 $244.55   5.183%   $257.225   $257.23   $257.25   $257.20  
  Purchase #5 $194.96   11.117%   $216.6337   $216.63   $216.65   $216.60  
  Purchase #6 $6.76   11.153%   $7.5139   $7.51   $7.50   $7.50  
  Purchase #7 $173.50   8.362%   $188.0081   $188.01   $188.00   $188.00  
  7 purchase totals = $1,024.06       $1,123.3516   $1,123.35   $1,123.40   $1,123.30