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 $218.45   8.347%   $236.684   $236.68   $236.70   $236.70  
  Purchase #2 $37.73   10.420%   $41.6615   $41.66   $41.65   $41.70  
  Purchase #3 $121.32   6.466%   $129.1646   $129.16   $129.15   $129.20  
  Purchase #4 $209.71   8.732%   $228.0219   $228.02   $228.00   $228.00  
  Purchase #5 $241.80   3.195%   $249.5255   $249.53   $249.55   $249.50  
  Purchase #6 $155.25   13.674%   $176.4789   $176.48   $176.50   $176.50  
  Purchase #7 $188.69   9.154%   $205.9627   $205.96   $205.95   $206.00  
  7 purchase totals = $1,172.95       $1,267.4991   $1,267.49   $1,267.50   $1,267.60