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 $56.79   8.762%   $61.7659   $61.77   $61.75   $61.80  
  Purchase #2 $182.52   6.798%   $194.9277   $194.93   $194.95   $194.90  
  Purchase #3 $26.49   7.699%   $28.5295   $28.53   $28.55   $28.50  
  Purchase #4 $38.31   13.727%   $43.5688   $43.57   $43.55   $43.60  
  Purchase #5 $130.96   9.647%   $143.5937   $143.59   $143.60   $143.60  
  Purchase #6 $248.43   13.371%   $281.6476   $281.65   $281.65   $281.60  
  Purchase #7 $215.30   6.219%   $228.6895   $228.69   $228.70   $228.70  
  7 purchase totals = $898.80       $982.7227   $982.73   $982.75   $982.70