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 $136.84   8.726%   $148.7807   $148.78   $148.80   $148.80  
  Purchase #2 $218.81   5.723%   $231.3325   $231.33   $231.35   $231.30  
  Purchase #3 $46.35   3.504%   $47.9741   $47.97   $47.95   $48.00  
  Purchase #4 $234.46   3.487%   $242.6356   $242.64   $242.65   $242.60  
  Purchase #5 $176.61   5.245%   $185.8732   $185.87   $185.85   $185.90  
  Purchase #6 $219.37   13.647%   $249.3074   $249.31   $249.30   $249.30  
  Purchase #7 $62.70   3.743%   $65.0469   $65.05   $65.05   $65.00  
  7 purchase totals = $1,095.14       $1,170.9504   $1,170.95   $1,170.95   $1,170.90