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 $220.67   10.659%   $244.1912   $244.19   $244.20   $244.20  
  Purchase #2 $212.79   9.794%   $233.6307   $233.63   $233.65   $233.60  
  Purchase #3 $194.53   8.441%   $210.9503   $210.95   $210.95   $211.00  
  Purchase #4 $76.43   3.738%   $79.287   $79.29   $79.30   $79.30  
  Purchase #5 $67.69   7.361%   $72.6727   $72.67   $72.65   $72.70  
  Purchase #6 $185.85   3.556%   $192.4588   $192.46   $192.45   $192.50  
  Purchase #7 $21.44   8.802%   $23.3271   $23.33   $23.35   $23.30  
  7 purchase totals = $979.40       $1,056.5178   $1,056.52   $1,056.55   $1,056.60