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	$39.61	7.837%	$42.7142	$42.71	$42.70	$42.70
Purchase #2	$53.89	9.550%	$59.0365	$59.04	$59.05	$59.00
Purchase #3	$241.54	10.634%	$267.2254	$267.23	$267.25	$267.20
Purchase #4	$25.44	13.187%	$28.7948	$28.79	$28.80	$28.80
Purchase #5	$182.47	4.271%	$190.2633	$190.26	$190.25	$190.30
Purchase #6	$33.53	6.500%	$35.7095	$35.71	$35.70	$35.70
Purchase #7	$222.79	5.220%	$234.4196	$234.42	$234.40	$234.40
7 purchase totals =	$799.27		$858.1633	$858.16	$858.15	$858.10