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 $147.53   13.302%   $167.1544   $167.15   $167.15   $167.20  
  Purchase #2 $64.82   5.769%   $68.5595   $68.56   $68.55   $68.60  
  Purchase #3 $229.91   8.723%   $249.965   $249.97   $249.95   $250.00  
  Purchase #4 $45.89   9.384%   $50.1963   $50.20   $50.20   $50.20  
  Purchase #5 $235.60   4.340%   $245.825   $245.83   $245.85   $245.80  
  Purchase #6 $61.40   7.441%   $65.9688   $65.97   $65.95   $66.00  
  Purchase #7 $24.76   8.647%   $26.901   $26.90   $26.90   $26.90  
  7 purchase totals = $809.91       $874.5700   $874.58   $874.55   $874.70