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 $156.80   8.733%   $170.4933   $170.49   $170.50   $170.50  
  Purchase #2 $229.97   7.152%   $246.4175   $246.42   $246.40   $246.40  
  Purchase #3 $111.84   3.311%   $115.543   $115.54   $115.55   $115.50  
  Purchase #4 $55.99   3.295%   $57.8349   $57.83   $57.85   $57.80  
  Purchase #5 $236.69   6.558%   $252.2121   $252.21   $252.20   $252.20  
  Purchase #6 $173.27   12.552%   $195.0189   $195.02   $195.00   $195.00  
  Purchase #7 $28.49   12.344%   $32.0068   $32.01   $32.00   $32.00  
  7 purchase totals = $993.05       $1,069.5265   $1,069.52   $1,069.50   $1,069.40