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 $81.93   11.823%   $91.6166   $91.62   $91.60   $91.60  
  Purchase #2 $48.64   10.108%   $53.5565   $53.56   $53.55   $53.60  
  Purchase #3 $122.74   8.178%   $132.7777   $132.78   $132.80   $132.80  
  Purchase #4 $95.41   10.652%   $105.5731   $105.57   $105.55   $105.60  
  Purchase #5 $177.69   9.185%   $194.0108   $194.01   $194.00   $194.00  
  Purchase #6 $222.64   12.301%   $250.0269   $250.03   $250.05   $250.00  
  Purchase #7 $38.39   13.825%   $43.6974   $43.70   $43.70   $43.70  
  7 purchase totals = $787.44       $871.2590   $871.27   $871.25   $871.30