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	$157.37	8.776%	$171.1808	$171.18	$171.20	$171.20
Purchase #2	$213.88	7.326%	$229.5488	$229.55	$229.55	$229.50
Purchase #3	$83.40	13.317%	$94.5064	$94.51	$94.50	$94.50
Purchase #4	$139.25	9.546%	$152.5428	$152.54	$152.55	$152.50
Purchase #5	$6.48	12.777%	$7.3079	$7.31	$7.30	$7.30
Purchase #6	$18.72	4.731%	$19.6056	$19.61	$19.60	$19.60
Purchase #7	$106.37	10.729%	$117.7824	$117.78	$117.80	$117.80
7 purchase totals =	$725.47		$792.4747	$792.48	$792.50	$792.40