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 $182.74   11.497%   $203.7496   $203.75   $203.75   $203.70  
  Purchase #2 $82.76   6.515%   $88.1518   $88.15   $88.15   $88.20  
  Purchase #3 $105.80   5.776%   $111.911   $111.91   $111.90   $111.90  
  Purchase #4 $196.79   5.330%   $207.2789   $207.28   $207.30   $207.30  
  Purchase #5 $103.40   13.289%   $117.1408   $117.14   $117.15   $117.10  
  Purchase #6 $111.88   6.470%   $119.1186   $119.12   $119.10   $119.10  
  Purchase #7 $107.54   5.276%   $113.2138   $113.21   $113.20   $113.20  
  7 purchase totals = $890.91       $960.5645   $960.56   $960.55   $960.50