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	$188.67	5.646%	$199.3223	$199.32	$199.30	$199.30
Purchase #2	$157.82	4.458%	$164.8556	$164.86	$164.85	$164.90
Purchase #3	$180.89	10.448%	$199.7894	$199.79	$199.80	$199.80
Purchase #4	$184.64	6.167%	$196.0267	$196.03	$196.05	$196.00
Purchase #5	$190.56	11.117%	$211.7446	$211.74	$211.75	$211.70
Purchase #6	$200.91	4.258%	$209.4647	$209.46	$209.45	$209.50
Purchase #7	$186.98	4.672%	$195.7157	$195.72	$195.70	$195.70
7 purchase totals =	$1,290.47		$1,376.9190	$1,376.92	$1,376.90	$1,376.90