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 $194.44   8.263%   $210.5066   $210.51   $210.50   $210.50  
  Purchase #2 $228.49   7.602%   $245.8598   $245.86   $245.85   $245.90  
  Purchase #3 $210.76   13.820%   $239.887   $239.89   $239.90   $239.90  
  Purchase #4 $168.76   8.753%   $183.5316   $183.53   $183.55   $183.50  
  Purchase #5 $158.32   9.175%   $172.8459   $172.85   $172.85   $172.80  
  Purchase #6 $63.54   11.646%   $70.9399   $70.94   $70.95   $70.90  
  Purchase #7 $125.35   7.122%   $134.2774   $134.28   $134.30   $134.30  
  7 purchase totals = $1,149.66       $1,257.8482   $1,257.86   $1,257.90   $1,257.80