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	$139.64	4.863%	$146.4307	$146.43	$146.45	$146.40
Purchase #2	$157.38	10.658%	$174.1536	$174.15	$174.15	$174.20
Purchase #3	$76.72	7.278%	$82.3037	$82.30	$82.30	$82.30
Purchase #4	$35.96	13.358%	$40.7635	$40.76	$40.75	$40.80
Purchase #5	$202.61	9.523%	$221.9046	$221.90	$221.90	$221.90
Purchase #6	$218.61	11.235%	$243.1708	$243.17	$243.15	$243.20
Purchase #7	$229.39	9.598%	$251.4069	$251.41	$251.40	$251.40
7 purchase totals =	$1,060.31		$1,160.1338	$1,160.12	$1,160.10	$1,160.20