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	$188.81	6.111%	$200.3482	$200.35	$200.35	$200.30
Purchase #2	$30.99	6.782%	$33.0917	$33.09	$33.10	$33.10
Purchase #3	$159.33	12.690%	$179.549	$179.55	$179.55	$179.50
Purchase #4	$183.74	3.693%	$190.5255	$190.53	$190.55	$190.50
Purchase #5	$220.76	10.521%	$243.9862	$243.99	$244.00	$244.00
Purchase #6	$71.53	9.228%	$78.1308	$78.13	$78.15	$78.10
Purchase #7	$5.73	12.170%	$6.4273	$6.43	$6.45	$6.40
7 purchase totals =	$860.89		$932.0587	$932.07	$932.15	$931.90