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	$190.35	12.226%	$213.6222	$213.62	$213.60	$213.60
Purchase #2	$244.67	9.489%	$267.8867	$267.89	$267.90	$267.90
Purchase #3	$30.50	6.277%	$32.4145	$32.41	$32.40	$32.40
Purchase #4	$75.77	7.355%	$81.3429	$81.34	$81.35	$81.30
Purchase #5	$89.80	10.281%	$99.0323	$99.03	$99.05	$99.00
Purchase #6	$150.75	10.414%	$166.4491	$166.45	$166.45	$166.40
Purchase #7	$43.76	3.110%	$45.1209	$45.12	$45.10	$45.10
7 purchase totals =	$825.60		$905.8686	$905.86	$905.85	$905.70