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	$42.90	5.648%	$45.323	$45.32	$45.30	$45.30
Purchase #2	$155.54	8.611%	$168.9335	$168.93	$168.95	$168.90
Purchase #3	$133.41	10.277%	$147.1205	$147.12	$147.10	$147.10
Purchase #4	$73.41	12.106%	$82.297	$82.30	$82.30	$82.30
Purchase #5	$137.53	10.192%	$151.5471	$151.55	$151.55	$151.50
Purchase #6	$100.64	9.597%	$110.2984	$110.30	$110.30	$110.30
Purchase #7	$90.34	10.346%	$99.6866	$99.69	$99.70	$99.70
7 purchase totals =	$733.77		$805.2061	$805.21	$805.20	$805.10