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	$79.50	12.234%	$89.226	$89.23	$89.25	$89.20
Purchase #2	$227.33	12.848%	$256.5374	$256.54	$256.55	$256.50
Purchase #3	$32.93	3.561%	$34.1026	$34.10	$34.10	$34.10
Purchase #4	$123.97	13.559%	$140.7791	$140.78	$140.80	$140.80
Purchase #5	$65.57	11.697%	$73.2397	$73.24	$73.25	$73.20
Purchase #6	$48.30	4.218%	$50.3373	$50.34	$50.35	$50.30
Purchase #7	$175.82	3.634%	$182.2093	$182.21	$182.20	$182.20
7 purchase totals =	$753.42		$826.4314	$826.44	$826.50	$826.30