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	$145.77	12.614%	$164.1574	$164.16	$164.15	$164.20
Purchase #2	$29.79	6.669%	$31.7767	$31.78	$31.80	$31.80
Purchase #3	$161.51	13.144%	$182.7389	$182.74	$182.75	$182.70
Purchase #4	$88.73	4.548%	$92.7654	$92.77	$92.75	$92.80
Purchase #5	$170.43	10.437%	$188.2178	$188.22	$188.20	$188.20
Purchase #6	$137.55	11.184%	$152.9336	$152.93	$152.95	$152.90
Purchase #7	$106.90	5.598%	$112.8843	$112.88	$112.90	$112.90
7 purchase totals =	$840.68		$925.4741	$925.48	$925.50	$925.50