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 $237.51   11.839%   $265.6288   $265.63   $265.65   $265.60  
  Purchase #2 $151.53   9.561%   $166.0178   $166.02   $166.00   $166.00  
  Purchase #3 $95.46   10.511%   $105.4938   $105.49   $105.50   $105.50  
  Purchase #4 $7.38   9.404%   $8.074   $8.07   $8.05   $8.10  
  Purchase #5 $58.94   10.421%   $65.0821   $65.08   $65.10   $65.10  
  Purchase #6 $246.71   5.182%   $259.4945   $259.49   $259.50   $259.50  
  Purchase #7 $221.92   11.448%   $247.3254   $247.33   $247.35   $247.30  
  7 purchase totals = $1,019.45       $1,117.1164   $1,117.11   $1,117.15   $1,117.10