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	$31.55	8.376%	$34.1926	$34.19	$34.20	$34.20
Purchase #2	$55.91	6.552%	$59.5732	$59.57	$59.55	$59.60
Purchase #3	$69.69	12.689%	$78.533	$78.53	$78.55	$78.50
Purchase #4	$79.34	11.386%	$88.3737	$88.37	$88.35	$88.40
Purchase #5	$141.55	9.431%	$154.8996	$154.90	$154.90	$154.90
Purchase #6	$137.47	6.840%	$146.8729	$146.87	$146.85	$146.90
Purchase #7	$37.28	7.316%	$40.0074	$40.01	$40.00	$40.00
7 purchase totals =	$552.79		$602.4524	$602.44	$602.40	$602.50