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 $82.86   11.277%   $92.2041   $92.20   $92.20   $92.20  
  Purchase #2 $71.29   7.790%   $76.8435   $76.84   $76.85   $76.80  
  Purchase #3 $221.63   13.669%   $251.9246   $251.92   $251.90   $251.90  
  Purchase #4 $36.59   12.289%   $41.0865   $41.09   $41.10   $41.10  
  Purchase #5 $70.62   3.785%   $73.293   $73.29   $73.30   $73.30  
  Purchase #6 $212.78   10.794%   $235.7475   $235.75   $235.75   $235.70  
  Purchase #7 $250.47   11.716%   $279.8151   $279.82   $279.80   $279.80  
  7 purchase totals = $946.24       $1,050.9143   $1,050.91   $1,050.90   $1,050.80