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	$72.32	7.865%	$78.008	$78.01	$78.00	$78.00
Purchase #2	$114.42	5.815%	$121.0735	$121.07	$121.05	$121.10
Purchase #3	$84.54	5.764%	$89.4129	$89.41	$89.40	$89.40
Purchase #4	$26.86	7.357%	$28.8361	$28.84	$28.85	$28.80
Purchase #5	$216.32	12.317%	$242.9641	$242.96	$242.95	$243.00
Purchase #6	$149.31	7.282%	$160.1828	$160.18	$160.20	$160.20
Purchase #7	$60.26	4.334%	$62.8717	$62.87	$62.85	$62.90
7 purchase totals =	$724.03		$783.3491	$783.34	$783.30	$783.40