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 $53.78   9.487%   $58.8821   $58.88   $58.90   $58.90  
  Purchase #2 $91.33   6.127%   $96.9258   $96.93   $96.95   $96.90  
  Purchase #3 $6.93   10.852%   $7.682   $7.68   $7.70   $7.70  
  Purchase #4 $210.72   7.681%   $226.9054   $226.91   $226.90   $226.90  
  Purchase #5 $61.52   4.144%   $64.0694   $64.07   $64.05   $64.10  
  Purchase #6 $185.53   4.784%   $194.4058   $194.41   $194.40   $194.40  
  Purchase #7 $128.87   5.766%   $136.3006   $136.30   $136.30   $136.30  
  7 purchase totals = $738.68       $785.1711   $785.18   $785.20   $785.20