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 $94.86   7.189%   $101.6795   $101.68   $101.70   $101.70  
  Purchase #2 $129.61   10.798%   $143.6053   $143.61   $143.60   $143.60  
  Purchase #3 $124.65   9.581%   $136.5927   $136.59   $136.60   $136.60  
  Purchase #4 $26.64   9.419%   $29.1492   $29.15   $29.15   $29.10  
  Purchase #5 $63.32   6.213%   $67.2541   $67.25   $67.25   $67.30  
  Purchase #6 $218.69   12.474%   $245.9694   $245.97   $245.95   $246.00  
  Purchase #7 $183.52   5.788%   $194.1421   $194.14   $194.15   $194.10  
  7 purchase totals = $841.29       $918.3923   $918.39   $918.40   $918.40