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 $100.59   12.841%   $113.5068   $113.51   $113.50   $113.50  
  Purchase #2 $246.54   10.628%   $272.7423   $272.74   $272.75   $272.70  
  Purchase #3 $181.53   13.442%   $205.9313   $205.93   $205.95   $205.90  
  Purchase #4 $88.60   8.583%   $96.2045   $96.20   $96.20   $96.20  
  Purchase #5 $99.67   11.223%   $110.856   $110.86   $110.85   $110.90  
  Purchase #6 $108.51   8.391%   $117.6151   $117.62   $117.60   $117.60  
  Purchase #7 $184.84   5.165%   $194.387   $194.39   $194.40   $194.40  
  7 purchase totals = $1,010.28       $1,111.2430   $1,111.25   $1,111.25   $1,111.20