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 $66.45   11.848%   $74.323   $74.32   $74.30   $74.30  
  Purchase #2 $212.54   10.491%   $234.8376   $234.84   $234.85   $234.80  
  Purchase #3 $167.64   4.692%   $175.5057   $175.51   $175.50   $175.50  
  Purchase #4 $243.61   13.602%   $276.7458   $276.75   $276.75   $276.70  
  Purchase #5 $55.63   7.669%   $59.8963   $59.90   $59.90   $59.90  
  Purchase #6 $229.68   3.506%   $237.7326   $237.73   $237.75   $237.70  
  Purchase #7 $205.48   6.590%   $219.0211   $219.02   $219.00   $219.00  
  7 purchase totals = $1,181.03       $1,278.0621   $1,278.07   $1,278.05   $1,277.90