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	$16.56	4.550%	$17.3135	$17.31	$17.30	$17.30
Purchase #2	$156.77	4.847%	$164.3686	$164.37	$164.35	$164.40
Purchase #3	$135.88	4.165%	$141.5394	$141.54	$141.55	$141.50
Purchase #4	$139.33	7.790%	$150.1838	$150.18	$150.20	$150.20
Purchase #5	$58.25	7.519%	$62.6298	$62.63	$62.65	$62.60
Purchase #6	$85.52	8.272%	$92.5942	$92.59	$92.60	$92.60
Purchase #7	$136.31	8.228%	$147.5256	$147.53	$147.55	$147.50
7 purchase totals =	$728.62		$776.1549	$776.15	$776.20	$776.10