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 $212.85   10.280%   $234.731   $234.73   $234.75   $234.70  
  Purchase #2 $33.93   8.750%   $36.8989   $36.90   $36.90   $36.90  
  Purchase #3 $126.30   3.420%   $130.6195   $130.62   $130.60   $130.60  
  Purchase #4 $6.99   8.645%   $7.5943   $7.59   $7.60   $7.60  
  Purchase #5 $191.35   11.543%   $213.4375   $213.44   $213.45   $213.40  
  Purchase #6 $188.41   8.696%   $204.7941   $204.79   $204.80   $204.80  
  Purchase #7 $215.43   13.566%   $244.6552   $244.66   $244.65   $244.70  
  7 purchase totals = $975.26       $1,072.7305   $1,072.73   $1,072.75   $1,072.70