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 $191.55   9.372%   $209.5021   $209.50   $209.50   $209.50  
  Purchase #2 $23.82   12.755%   $26.8582   $26.86   $26.85   $26.90  
  Purchase #3 $52.81   13.588%   $59.9858   $59.99   $60.00   $60.00  
  Purchase #4 $173.47   5.190%   $182.4731   $182.47   $182.45   $182.50  
  Purchase #5 $155.39   12.802%   $175.283   $175.28   $175.30   $175.30  
  Purchase #6 $8.53   12.330%   $9.5817   $9.58   $9.60   $9.60  
  Purchase #7 $219.46   11.519%   $244.7396   $244.74   $244.75   $244.70  
  7 purchase totals = $825.03       $908.4235   $908.42   $908.45   $908.50