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	$6.98	6.626%	$7.4425	$7.44	$7.45	$7.40
Purchase #2	$134.36	12.316%	$150.9078	$150.91	$150.90	$150.90
Purchase #3	$61.71	9.403%	$67.5126	$67.51	$67.50	$67.50
Purchase #4	$236.31	8.139%	$255.5433	$255.54	$255.55	$255.50
Purchase #5	$208.64	7.465%	$224.215	$224.22	$224.20	$224.20
Purchase #6	$147.74	4.548%	$154.4592	$154.46	$154.45	$154.50
Purchase #7	$152.32	5.782%	$161.1271	$161.13	$161.15	$161.10
7 purchase totals =	$948.06		$1,021.2075	$1,021.21	$1,021.20	$1,021.10