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 $97.49   6.627%   $103.9507   $103.95   $103.95   $104.00  
  Purchase #2 $188.50   7.782%   $203.1691   $203.17   $203.15   $203.20  
  Purchase #3 $103.48   10.651%   $114.5017   $114.50   $114.50   $114.50  
  Purchase #4 $64.88   12.281%   $72.8479   $72.85   $72.85   $72.80  
  Purchase #5 $212.84   10.659%   $235.5266   $235.53   $235.55   $235.50  
  Purchase #6 $87.29   8.173%   $94.4242   $94.42   $94.40   $94.40  
  Purchase #7 $72.61   13.264%   $82.241   $82.24   $82.25   $82.20  
  7 purchase totals = $827.09       $906.6612   $906.66   $906.65   $906.60