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	$121.50	10.543%	$134.3097	$134.31	$134.30	$134.30
Purchase #2	$219.55	6.172%	$233.1006	$233.10	$233.10	$233.10
Purchase #3	$112.44	10.400%	$124.1338	$124.13	$124.15	$124.10
Purchase #4	$140.36	10.755%	$155.4557	$155.46	$155.45	$155.50
Purchase #5	$142.39	6.147%	$151.1427	$151.14	$151.15	$151.10
Purchase #6	$164.56	7.401%	$176.7391	$176.74	$176.75	$176.70
Purchase #7	$169.59	9.571%	$185.8215	$185.82	$185.80	$185.80
7 purchase totals =	$1,070.39		$1,160.7031	$1,160.70	$1,160.70	$1,160.60