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	$135.92	11.364%	$151.3659	$151.37	$151.35	$151.40
Purchase #2	$41.56	9.363%	$45.4513	$45.45	$45.45	$45.50
Purchase #3	$233.76	4.138%	$243.433	$243.43	$243.45	$243.40
Purchase #4	$35.34	11.432%	$39.3801	$39.38	$39.40	$39.40
Purchase #5	$177.48	6.251%	$188.5743	$188.57	$188.55	$188.60
Purchase #6	$67.82	8.655%	$73.6898	$73.69	$73.70	$73.70
Purchase #7	$83.59	7.639%	$89.9754	$89.98	$90.00	$90.00
7 purchase totals =	$775.47		$831.8698	$831.87	$831.90	$832.00