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	$31.89	4.442%	$33.3066	$33.31	$33.30	$33.30
Purchase #2	$148.61	13.407%	$168.5341	$168.53	$168.55	$168.50
Purchase #3	$84.36	3.213%	$87.0705	$87.07	$87.05	$87.10
Purchase #4	$48.95	8.384%	$53.054	$53.05	$53.05	$53.10
Purchase #5	$54.44	8.490%	$59.062	$59.06	$59.05	$59.10
Purchase #6	$109.86	13.574%	$124.7724	$124.77	$124.75	$124.80
Purchase #7	$20.46	11.306%	$22.7732	$22.77	$22.75	$22.80
7 purchase totals =	$498.57		$548.5728	$548.56	$548.50	$548.70