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	$93.86	6.454%	$99.9177	$99.92	$99.90	$99.90
Purchase #2	$133.74	10.503%	$147.7867	$147.79	$147.80	$147.80
Purchase #3	$55.91	6.694%	$59.6526	$59.65	$59.65	$59.70
Purchase #4	$56.83	8.183%	$61.4804	$61.48	$61.50	$61.50
Purchase #5	$35.42	4.412%	$36.9827	$36.98	$37.00	$37.00
Purchase #6	$119.95	9.375%	$131.1953	$131.20	$131.20	$131.20
Purchase #7	$127.92	7.574%	$137.6087	$137.61	$137.60	$137.60
7 purchase totals =	$623.63		$674.6241	$674.63	$674.65	$674.70