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	$87.31	4.684%	$91.3996	$91.40	$91.40	$91.40
Purchase #2	$234.70	6.743%	$250.5258	$250.53	$250.55	$250.50
Purchase #3	$130.37	4.149%	$135.7791	$135.78	$135.80	$135.80
Purchase #4	$38.96	12.779%	$43.9387	$43.94	$43.95	$43.90
Purchase #5	$125.71	13.588%	$142.7915	$142.79	$142.80	$142.80
Purchase #6	$103.83	13.199%	$117.5345	$117.53	$117.55	$117.50
Purchase #7	$118.66	7.765%	$127.8739	$127.87	$127.85	$127.90
7 purchase totals =	$839.54		$909.8431	$909.84	$909.90	$909.80