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	$102.45	8.546%	$111.2054	$111.21	$111.20	$111.20
Purchase #2	$221.73	13.623%	$251.9363	$251.94	$251.95	$251.90
Purchase #3	$133.65	10.294%	$147.4079	$147.41	$147.40	$147.40
Purchase #4	$250.81	9.738%	$275.2339	$275.23	$275.25	$275.20
Purchase #5	$63.71	11.826%	$71.2443	$71.24	$71.25	$71.20
Purchase #6	$39.76	7.870%	$42.8891	$42.89	$42.90	$42.90
Purchase #7	$71.47	3.436%	$73.9257	$73.93	$73.95	$73.90
7 purchase totals =	$883.58		$973.8426	$973.85	$973.90	$973.70