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 $148.94   3.222%   $153.7388   $153.74   $153.75   $153.70  
  Purchase #2 $137.85   11.457%   $153.6435   $153.64   $153.65   $153.60  
  Purchase #3 $211.79   6.555%   $225.6728   $225.67   $225.65   $225.70  
  Purchase #4 $92.54   6.105%   $98.1896   $98.19   $98.20   $98.20  
  Purchase #5 $219.32   8.345%   $237.6223   $237.62   $237.60   $237.60  
  Purchase #6 $149.36   11.430%   $166.4318   $166.43   $166.45   $166.40  
  Purchase #7 $167.61   6.727%   $178.8851   $178.89   $178.90   $178.90  
  7 purchase totals = $1,127.41       $1,214.1839   $1,214.18   $1,214.20   $1,214.10