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	$125.92	6.846%	$134.5405	$134.54	$134.55	$134.50
Purchase #2	$132.72	3.535%	$137.4117	$137.41	$137.40	$137.40
Purchase #3	$172.59	8.244%	$186.8183	$186.82	$186.80	$186.80
Purchase #4	$82.70	6.873%	$88.384	$88.38	$88.40	$88.40
Purchase #5	$111.70	7.399%	$119.9647	$119.96	$119.95	$120.00
Purchase #6	$170.43	11.212%	$189.5386	$189.54	$189.55	$189.50
Purchase #7	$236.55	7.581%	$254.4829	$254.48	$254.50	$254.50
7 purchase totals =	$1,032.61		$1,111.1407	$1,111.13	$1,111.15	$1,111.10