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	$120.66	12.129%	$135.2949	$135.29	$135.30	$135.30
Purchase #2	$84.84	4.700%	$88.8275	$88.83	$88.85	$88.80
Purchase #3	$159.90	5.273%	$168.3315	$168.33	$168.35	$168.30
Purchase #4	$196.91	8.249%	$213.1531	$213.15	$213.15	$213.20
Purchase #5	$60.32	11.624%	$67.3316	$67.33	$67.35	$67.30
Purchase #6	$150.78	10.451%	$166.538	$166.54	$166.55	$166.50
Purchase #7	$238.89	7.223%	$256.145	$256.15	$256.15	$256.10
7 purchase totals =	$1,012.30		$1,095.6216	$1,095.62	$1,095.70	$1,095.50