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	$71.81	9.574%	$78.6851	$78.69	$78.70	$78.70
Purchase #2	$97.37	4.666%	$101.9133	$101.91	$101.90	$101.90
Purchase #3	$150.36	7.607%	$161.7979	$161.80	$161.80	$161.80
Purchase #4	$53.88	13.522%	$61.1657	$61.17	$61.15	$61.20
Purchase #5	$165.87	3.587%	$171.8198	$171.82	$171.80	$171.80
Purchase #6	$52.60	9.817%	$57.7637	$57.76	$57.75	$57.80
Purchase #7	$86.80	3.447%	$89.792	$89.79	$89.80	$89.80
7 purchase totals =	$678.69		$722.9375	$722.94	$722.90	$723.00