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	$45.95	11.802%	$51.373	$51.37	$51.35	$51.40
Purchase #2	$91.47	4.779%	$95.8414	$95.84	$95.85	$95.80
Purchase #3	$119.49	3.174%	$123.2826	$123.28	$123.30	$123.30
Purchase #4	$83.28	6.318%	$88.5416	$88.54	$88.55	$88.50
Purchase #5	$22.31	4.833%	$23.3882	$23.39	$23.40	$23.40
Purchase #6	$67.70	7.138%	$72.5324	$72.53	$72.55	$72.50
Purchase #7	$31.94	6.306%	$33.9541	$33.95	$33.95	$34.00
7 purchase totals =	$462.14		$488.9133	$488.90	$488.95	$488.90