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 $53.49   8.328%   $57.9446   $57.94   $57.95   $57.90  
  Purchase #2 $25.59   11.659%   $28.5735   $28.57   $28.55   $28.60  
  Purchase #3 $124.52   8.687%   $135.3371   $135.34   $135.35   $135.30  
  Purchase #4 $111.62   5.478%   $117.7345   $117.73   $117.75   $117.70  
  Purchase #5 $198.99   11.846%   $222.5624   $222.56   $222.55   $222.60  
  Purchase #6 $226.26   10.757%   $250.5988   $250.60   $250.60   $250.60  
  Purchase #7 $181.78   6.759%   $194.0665   $194.07   $194.05   $194.10  
  7 purchase totals = $922.25       $1,006.8174   $1,006.81   $1,006.80   $1,006.80