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	$20.79	4.795%	$21.7869	$21.79	$21.80	$21.80
Purchase #2	$185.63	10.369%	$204.878	$204.88	$204.90	$204.90
Purchase #3	$115.90	8.356%	$125.5846	$125.58	$125.60	$125.60
Purchase #4	$246.82	7.158%	$264.4874	$264.49	$264.50	$264.50
Purchase #5	$79.50	5.234%	$83.661	$83.66	$83.65	$83.70
Purchase #6	$107.99	8.768%	$117.4586	$117.46	$117.45	$117.50
Purchase #7	$179.26	3.572%	$185.6632	$185.66	$185.65	$185.70
7 purchase totals =	$935.89		$1,003.5197	$1,003.52	$1,003.55	$1,003.70