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	$157.86	8.496%	$171.2718	$171.27	$171.25	$171.30
Purchase #2	$61.71	13.489%	$70.0341	$70.03	$70.05	$70.00
Purchase #3	$177.82	6.237%	$188.9106	$188.91	$188.90	$188.90
Purchase #4	$88.59	12.803%	$99.9322	$99.93	$99.95	$99.90
Purchase #5	$64.78	13.254%	$73.3659	$73.37	$73.35	$73.40
Purchase #6	$20.87	3.367%	$21.5727	$21.57	$21.55	$21.60
Purchase #7	$223.46	8.802%	$243.1289	$243.13	$243.15	$243.10
7 purchase totals =	$795.09		$868.2162	$868.21	$868.20	$868.20