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	$152.55	12.672%	$171.8811	$171.88	$171.90	$171.90
Purchase #2	$53.82	10.680%	$59.568	$59.57	$59.55	$59.60
Purchase #3	$41.61	6.483%	$44.3076	$44.31	$44.30	$44.30
Purchase #4	$80.54	13.203%	$91.1737	$91.17	$91.15	$91.20
Purchase #5	$48.71	7.803%	$52.5108	$52.51	$52.50	$52.50
Purchase #6	$136.54	4.560%	$142.7662	$142.77	$142.75	$142.80
Purchase #7	$101.67	11.205%	$113.0621	$113.06	$113.05	$113.10
7 purchase totals =	$615.44		$675.2695	$675.27	$675.20	$675.40