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	$41.43	4.777%	$43.4091	$43.41	$43.40	$43.40
Purchase #2	$89.78	9.594%	$98.3935	$98.39	$98.40	$98.40
Purchase #3	$169.64	6.217%	$180.1865	$180.19	$180.20	$180.20
Purchase #4	$76.33	11.764%	$85.3095	$85.31	$85.30	$85.30
Purchase #5	$153.79	10.695%	$170.2378	$170.24	$170.25	$170.20
Purchase #6	$37.42	11.590%	$41.757	$41.76	$41.75	$41.80
Purchase #7	$123.55	12.786%	$139.3471	$139.35	$139.35	$139.30
7 purchase totals =	$691.94		$758.6405	$758.65	$758.65	$758.60