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	$250.49	3.468%	$259.177	$259.18	$259.20	$259.20
Purchase #2	$110.74	10.415%	$122.2736	$122.27	$122.25	$122.30
Purchase #3	$37.36	11.211%	$41.5484	$41.55	$41.55	$41.50
Purchase #4	$68.79	3.460%	$71.1701	$71.17	$71.15	$71.20
Purchase #5	$36.69	13.348%	$41.5874	$41.59	$41.60	$41.60
Purchase #6	$218.47	13.735%	$248.4769	$248.48	$248.50	$248.50
Purchase #7	$84.47	7.306%	$90.6414	$90.64	$90.65	$90.60
7 purchase totals =	$807.01		$874.8748	$874.88	$874.90	$874.90