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 $113.86   13.742%   $129.5066   $129.51   $129.50   $129.50  
  Purchase #2 $136.99   12.372%   $153.9384   $153.94   $153.95   $153.90  
  Purchase #3 $214.98   3.493%   $222.4893   $222.49   $222.50   $222.50  
  Purchase #4 $150.92   10.599%   $166.916   $166.92   $166.90   $166.90  
  Purchase #5 $226.73   8.620%   $246.2741   $246.27   $246.25   $246.30  
  Purchase #6 $220.79   7.154%   $236.5853   $236.59   $236.60   $236.60  
  Purchase #7 $35.61   10.380%   $39.3063   $39.31   $39.30   $39.30  
  7 purchase totals = $1,099.88       $1,195.0160   $1,195.03   $1,195.00   $1,195.00