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 $82.34   7.420%   $88.4496   $88.45   $88.45   $88.40  
  Purchase #2 $211.38   8.191%   $228.6941   $228.69   $228.70   $228.70  
  Purchase #3 $103.30   4.478%   $107.9258   $107.93   $107.95   $107.90  
  Purchase #4 $70.38   6.800%   $75.1658   $75.17   $75.15   $75.20  
  Purchase #5 $221.92   5.181%   $233.4177   $233.42   $233.40   $233.40  
  Purchase #6 $71.78   12.190%   $80.53   $80.53   $80.55   $80.50  
  Purchase #7 $120.94   4.857%   $126.8141   $126.81   $126.80   $126.80  
  7 purchase totals = $882.04       $940.9971   $941.00   $941.00   $940.90