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 $61.54   8.166%   $66.5654   $66.57   $66.55   $66.60  
  Purchase #2 $155.44   11.609%   $173.485   $173.49   $173.50   $173.50  
  Purchase #3 $207.79   9.221%   $226.9503   $226.95   $226.95   $227.00  
  Purchase #4 $93.76   3.596%   $97.1316   $97.13   $97.15   $97.10  
  Purchase #5 $245.94   13.251%   $278.5295   $278.53   $278.55   $278.50  
  Purchase #6 $132.59   4.492%   $138.5459   $138.55   $138.55   $138.50  
  Purchase #7 $124.25   12.521%   $139.8073   $139.81   $139.80   $139.80  
  7 purchase totals = $1,021.31       $1,121.0150   $1,121.03   $1,121.05   $1,121.00