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	$159.38	7.422%	$171.2092	$171.21	$171.20	$171.20
Purchase #2	$83.54	9.263%	$91.2783	$91.28	$91.30	$91.30
Purchase #3	$45.86	13.815%	$52.1956	$52.20	$52.20	$52.20
Purchase #4	$28.41	11.658%	$31.722	$31.72	$31.70	$31.70
Purchase #5	$24.36	11.435%	$27.1456	$27.15	$27.15	$27.10
Purchase #6	$240.61	6.224%	$255.5856	$255.59	$255.60	$255.60
Purchase #7	$33.49	10.415%	$36.978	$36.98	$37.00	$37.00
7 purchase totals =	$615.65		$666.1143	$666.13	$666.15	$666.10