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	$40.68	12.780%	$45.8789	$45.88	$45.90	$45.90
Purchase #2	$112.91	9.428%	$123.5552	$123.56	$123.55	$123.60
Purchase #3	$41.96	3.235%	$43.3174	$43.32	$43.30	$43.30
Purchase #4	$211.89	7.654%	$228.1081	$228.11	$228.10	$228.10
Purchase #5	$98.70	4.452%	$103.0941	$103.09	$103.10	$103.10
Purchase #6	$101.87	11.153%	$113.2316	$113.23	$113.25	$113.20
Purchase #7	$5.59	12.588%	$6.2937	$6.29	$6.30	$6.30
7 purchase totals =	$613.60		$663.4790	$663.48	$663.50	$663.50