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	$35.30	6.164%	$37.4759	$37.48	$37.50	$37.50
Purchase #2	$79.49	3.864%	$82.5615	$82.56	$82.55	$82.60
Purchase #3	$165.91	13.687%	$188.6181	$188.62	$188.60	$188.60
Purchase #4	$81.30	9.780%	$89.2511	$89.25	$89.25	$89.30
Purchase #5	$121.63	7.465%	$130.7097	$130.71	$130.70	$130.70
Purchase #6	$247.36	8.371%	$268.0665	$268.07	$268.05	$268.10
Purchase #7	$79.89	9.347%	$87.3573	$87.36	$87.35	$87.40
7 purchase totals =	$810.88		$884.0401	$884.05	$884.00	$884.20