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	$215.77	3.179%	$222.6293	$222.63	$222.65	$222.60
Purchase #2	$81.44	11.447%	$90.7624	$90.76	$90.75	$90.80
Purchase #3	$220.33	10.394%	$243.2311	$243.23	$243.25	$243.20
Purchase #4	$67.26	3.338%	$69.5051	$69.51	$69.50	$69.50
Purchase #5	$83.78	6.545%	$89.2634	$89.26	$89.25	$89.30
Purchase #6	$43.53	8.332%	$47.1569	$47.16	$47.15	$47.20
Purchase #7	$65.71	9.126%	$71.7067	$71.71	$71.70	$71.70
7 purchase totals =	$777.82		$834.2549	$834.26	$834.25	$834.30