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	$8.57	6.850%	$9.157	$9.16	$9.15	$9.20
Purchase #2	$79.62	4.149%	$82.9234	$82.92	$82.90	$82.90
Purchase #3	$50.33	8.253%	$54.4837	$54.48	$54.50	$54.50
Purchase #4	$134.37	13.362%	$152.3245	$152.32	$152.30	$152.30
Purchase #5	$66.44	4.402%	$69.3647	$69.36	$69.35	$69.40
Purchase #6	$56.82	7.811%	$61.2582	$61.26	$61.25	$61.30
Purchase #7	$152.89	8.396%	$165.7266	$165.73	$165.75	$165.70
7 purchase totals =	$549.04		$595.2381	$595.23	$595.20	$595.30