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	$171.54	4.646%	$179.5097	$179.51	$179.50	$179.50
Purchase #2	$75.41	10.483%	$83.3152	$83.32	$83.30	$83.30
Purchase #3	$92.49	10.414%	$102.1219	$102.12	$102.10	$102.10
Purchase #4	$12.71	11.228%	$14.1371	$14.14	$14.15	$14.10
Purchase #5	$135.86	5.606%	$143.4763	$143.48	$143.50	$143.50
Purchase #6	$222.95	4.447%	$232.8646	$232.86	$232.85	$232.90
Purchase #7	$160.37	9.686%	$175.9034	$175.90	$175.90	$175.90
7 purchase totals =	$871.33		$931.3282	$931.33	$931.30	$931.30