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	$6.58	11.524%	$7.3383	$7.34	$7.35	$7.30
Purchase #2	$82.26	13.755%	$93.5749	$93.57	$93.55	$93.60
Purchase #3	$229.69	10.510%	$253.8304	$253.83	$253.85	$253.80
Purchase #4	$150.77	13.559%	$171.2129	$171.21	$171.20	$171.20
Purchase #5	$35.98	10.749%	$39.8475	$39.85	$39.85	$39.80
Purchase #6	$39.89	13.797%	$45.3936	$45.39	$45.40	$45.40
Purchase #7	$48.29	12.288%	$54.2239	$54.22	$54.20	$54.20
7 purchase totals =	$593.46		$665.4215	$665.41	$665.40	$665.30