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	$188.99	12.473%	$212.5627	$212.56	$212.55	$212.60
Purchase #2	$32.76	8.561%	$35.5646	$35.56	$35.55	$35.60
Purchase #3	$228.57	7.555%	$245.8385	$245.84	$245.85	$245.80
Purchase #4	$119.70	6.802%	$127.842	$127.84	$127.85	$127.80
Purchase #5	$133.51	13.331%	$151.3082	$151.31	$151.30	$151.30
Purchase #6	$122.36	7.501%	$131.5382	$131.54	$131.55	$131.50
Purchase #7	$103.41	9.208%	$112.932	$112.93	$112.95	$112.90
7 purchase totals =	$929.30		$1,017.5862	$1,017.58	$1,017.60	$1,017.50