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 $207.56   13.357%   $235.2838   $235.28   $235.30   $235.30  
  Purchase #2 $47.84   12.810%   $53.9683   $53.97   $53.95   $54.00  
  Purchase #3 $236.81   7.813%   $255.312   $255.31   $255.30   $255.30  
  Purchase #4 $14.90   6.517%   $15.871   $15.87   $15.85   $15.90  
  Purchase #5 $131.68   3.109%   $135.7739   $135.77   $135.75   $135.80  
  Purchase #6 $159.58   12.410%   $179.3839   $179.38   $179.40   $179.40  
  Purchase #7 $184.78   4.717%   $193.4961   $193.50   $193.50   $193.50  
  7 purchase totals = $983.15       $1,069.0890   $1,069.08   $1,069.05   $1,069.20