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	$223.80	13.290%	$253.543	$253.54	$253.55	$253.50
Purchase #2	$119.25	9.821%	$130.9615	$130.96	$130.95	$131.00
Purchase #3	$86.28	5.324%	$90.8735	$90.87	$90.85	$90.90
Purchase #4	$82.30	3.267%	$84.9887	$84.99	$85.00	$85.00
Purchase #5	$101.45	7.127%	$108.6803	$108.68	$108.70	$108.70
Purchase #6	$98.96	6.573%	$105.4646	$105.46	$105.45	$105.50
Purchase #7	$72.78	6.491%	$77.5041	$77.50	$77.50	$77.50
7 purchase totals =	$784.82		$852.0157	$852.00	$852.00	$852.10