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 $194.95   12.236%   $218.8041   $218.80   $218.80   $218.80  
  Purchase #2 $178.28   9.587%   $195.3717   $195.37   $195.35   $195.40  
  Purchase #3 $68.35   12.347%   $76.7892   $76.79   $76.80   $76.80  
  Purchase #4 $238.66   5.189%   $251.0441   $251.04   $251.05   $251.00  
  Purchase #5 $17.39   3.119%   $17.9324   $17.93   $17.95   $17.90  
  Purchase #6 $101.66   7.427%   $109.2103   $109.21   $109.20   $109.20  
  Purchase #7 $128.74   13.336%   $145.9088   $145.91   $145.90   $145.90  
  7 purchase totals = $928.03       $1,015.0606   $1,015.05   $1,015.05   $1,015.00