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	$28.74	8.519%	$31.1884	$31.19	$31.20	$31.20
Purchase #2	$191.60	3.809%	$198.898	$198.90	$198.90	$198.90
Purchase #3	$78.58	4.840%	$82.3833	$82.38	$82.40	$82.40
Purchase #4	$184.82	3.657%	$191.5789	$191.58	$191.60	$191.60
Purchase #5	$94.99	11.152%	$105.5833	$105.58	$105.60	$105.60
Purchase #6	$186.57	11.832%	$208.645	$208.65	$208.65	$208.60
Purchase #7	$147.37	4.198%	$153.5566	$153.56	$153.55	$153.60
7 purchase totals =	$912.67		$971.8335	$971.84	$971.90	$971.90