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	$37.68	5.716%	$39.8338	$39.83	$39.85	$39.80
Purchase #2	$110.70	11.738%	$123.694	$123.69	$123.70	$123.70
Purchase #3	$64.84	13.322%	$73.478	$73.48	$73.50	$73.50
Purchase #4	$225.30	9.140%	$245.8924	$245.89	$245.90	$245.90
Purchase #5	$149.74	3.512%	$154.9989	$155.00	$155.00	$155.00
Purchase #6	$96.67	13.635%	$109.851	$109.85	$109.85	$109.90
Purchase #7	$79.98	12.146%	$89.6944	$89.69	$89.70	$89.70
7 purchase totals =	$764.91		$837.4425	$837.43	$837.50	$837.50