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	$176.56	5.216%	$185.7694	$185.77	$185.75	$185.80
Purchase #2	$38.26	5.363%	$40.3119	$40.31	$40.30	$40.30
Purchase #3	$164.61	10.797%	$182.3829	$182.38	$182.40	$182.40
Purchase #4	$71.26	10.461%	$78.7145	$78.71	$78.70	$78.70
Purchase #5	$250.62	6.505%	$266.9228	$266.92	$266.90	$266.90
Purchase #6	$187.80	12.109%	$210.5407	$210.54	$210.55	$210.50
Purchase #7	$59.55	12.593%	$67.0491	$67.05	$67.05	$67.00
7 purchase totals =	$948.66		$1,031.6913	$1,031.68	$1,031.65	$1,031.60