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 $136.69   10.692%   $151.3049   $151.30   $151.30   $151.30  
  Purchase #2 $29.74   8.597%   $32.2967   $32.30   $32.30   $32.30  
  Purchase #3 $172.87   5.453%   $182.2966   $182.30   $182.30   $182.30  
  Purchase #4 $192.55   10.611%   $212.9815   $212.98   $213.00   $213.00  
  Purchase #5 $14.72   5.365%   $15.5097   $15.51   $15.50   $15.50  
  Purchase #6 $140.77   13.592%   $159.9035   $159.90   $159.90   $159.90  
  Purchase #7 $244.88   9.592%   $268.3689   $268.37   $268.35   $268.40  
  7 purchase totals = $932.22       $1,022.6618   $1,022.66   $1,022.65   $1,022.70