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 $55.99   8.261%   $60.6153   $60.62   $60.60   $60.60  
  Purchase #2 $240.57   6.516%   $256.2455   $256.25   $256.25   $256.20  
  Purchase #3 $240.64   13.778%   $273.7954   $273.80   $273.80   $273.80  
  Purchase #4 $117.83   7.377%   $126.5223   $126.52   $126.50   $126.50  
  Purchase #5 $120.91   10.263%   $133.319   $133.32   $133.30   $133.30  
  Purchase #6 $60.36   11.851%   $67.5133   $67.51   $67.50   $67.50  
  Purchase #7 $121.41   12.153%   $136.165   $136.17   $136.15   $136.20  
  7 purchase totals = $957.71       $1,054.1758   $1,054.19   $1,054.10   $1,054.10