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	$244.55	11.807%	$273.424	$273.42	$273.40	$273.40
Purchase #2	$194.31	11.519%	$216.6926	$216.69	$216.70	$216.70
Purchase #3	$35.78	9.598%	$39.2142	$39.21	$39.20	$39.20
Purchase #4	$38.72	8.862%	$42.1514	$42.15	$42.15	$42.20
Purchase #5	$75.89	12.469%	$85.3527	$85.35	$85.35	$85.40
Purchase #6	$81.84	8.163%	$88.5206	$88.52	$88.50	$88.50
Purchase #7	$208.72	11.668%	$233.0734	$233.07	$233.05	$233.10
7 purchase totals =	$879.81		$978.4289	$978.41	$978.35	$978.50