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	$55.27	5.139%	$58.1103	$58.11	$58.10	$58.10
Purchase #2	$137.61	3.240%	$142.0686	$142.07	$142.05	$142.10
Purchase #3	$236.31	6.302%	$251.2023	$251.20	$251.20	$251.20
Purchase #4	$36.62	3.275%	$37.8193	$37.82	$37.80	$37.80
Purchase #5	$83.40	10.190%	$91.8985	$91.90	$91.90	$91.90
Purchase #6	$82.60	8.507%	$89.6268	$89.63	$89.65	$89.60
Purchase #7	$105.55	3.739%	$109.4965	$109.50	$109.50	$109.50
7 purchase totals =	$737.36		$780.2223	$780.23	$780.20	$780.20