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	$50.87	6.107%	$53.9766	$53.98	$54.00	$54.00
Purchase #2	$120.66	7.183%	$129.327	$129.33	$129.35	$129.30
Purchase #3	$129.89	12.308%	$145.8769	$145.88	$145.90	$145.90
Purchase #4	$158.59	4.621%	$165.9184	$165.92	$165.90	$165.90
Purchase #5	$76.78	8.626%	$83.403	$83.40	$83.40	$83.40
Purchase #6	$106.37	13.213%	$120.4247	$120.42	$120.40	$120.40
Purchase #7	$228.94	6.372%	$243.5281	$243.53	$243.55	$243.50
7 purchase totals =	$872.10		$942.4547	$942.46	$942.50	$942.40