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	$32.51	3.567%	$33.6696	$33.67	$33.65	$33.70
Purchase #2	$162.96	10.408%	$179.9209	$179.92	$179.90	$179.90
Purchase #3	$136.51	10.240%	$150.4886	$150.49	$150.50	$150.50
Purchase #4	$89.78	12.131%	$100.6712	$100.67	$100.65	$100.70
Purchase #5	$77.36	6.735%	$82.5702	$82.57	$82.55	$82.60
Purchase #6	$164.64	7.310%	$176.6752	$176.68	$176.70	$176.70
Purchase #7	$120.75	8.306%	$130.7795	$130.78	$130.80	$130.80
7 purchase totals =	$784.51		$854.7752	$854.78	$854.75	$854.90