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 $15.67   10.152%   $17.2608   $17.26   $17.25   $17.30  
  Purchase #2 $211.76   6.617%   $225.7722   $225.77   $225.75   $225.80  
  Purchase #3 $171.82   6.359%   $182.746   $182.75   $182.75   $182.70  
  Purchase #4 $23.76   10.580%   $26.2738   $26.27   $26.25   $26.30  
  Purchase #5 $199.60   9.736%   $219.0331   $219.03   $219.05   $219.00  
  Purchase #6 $174.80   5.339%   $184.1326   $184.13   $184.15   $184.10  
  Purchase #7 $65.60   11.613%   $73.2181   $73.22   $73.20   $73.20  
  7 purchase totals = $863.01       $928.4366   $928.43   $928.40   $928.40