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	$116.79	6.441%	$124.3124	$124.31	$124.30	$124.30
Purchase #2	$69.55	3.381%	$71.9015	$71.90	$71.90	$71.90
Purchase #3	$69.67	3.228%	$71.9189	$71.92	$71.90	$71.90
Purchase #4	$225.81	9.344%	$246.9097	$246.91	$246.90	$246.90
Purchase #5	$229.44	11.468%	$255.7522	$255.75	$255.75	$255.80
Purchase #6	$65.81	9.661%	$72.1679	$72.17	$72.15	$72.20
Purchase #7	$247.71	12.453%	$278.5573	$278.56	$278.55	$278.60
7 purchase totals =	$1,024.78		$1,121.5199	$1,121.52	$1,121.45	$1,121.60