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 $54.84   6.857%   $58.6004   $58.60   $58.60   $58.60  
  Purchase #2 $150.92   10.648%   $166.99   $166.99   $167.00   $167.00  
  Purchase #3 $126.57   3.374%   $130.8405   $130.84   $130.85   $130.80  
  Purchase #4 $38.80   12.525%   $43.6597   $43.66   $43.65   $43.70  
  Purchase #5 $167.27   9.368%   $182.9399   $182.94   $182.95   $182.90  
  Purchase #6 $131.32   3.683%   $136.1565   $136.16   $136.15   $136.20  
  Purchase #7 $110.38   3.206%   $113.9188   $113.92   $113.90   $113.90  
  7 purchase totals = $780.10       $833.1058   $833.11   $833.10   $833.10