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	$25.94	11.382%	$28.8925	$28.89	$28.90	$28.90
Purchase #2	$13.57	6.711%	$14.4807	$14.48	$14.50	$14.50
Purchase #3	$188.93	7.676%	$203.4323	$203.43	$203.45	$203.40
Purchase #4	$247.93	11.236%	$275.7874	$275.79	$275.80	$275.80
Purchase #5	$82.25	11.252%	$91.5048	$91.50	$91.50	$91.50
Purchase #6	$86.34	7.669%	$92.9614	$92.96	$92.95	$93.00
Purchase #7	$247.27	9.695%	$271.2428	$271.24	$271.25	$271.20
7 purchase totals =	$892.23		$978.3019	$978.29	$978.35	$978.30