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	$126.32	8.364%	$136.8854	$136.89	$136.90	$136.90
Purchase #2	$149.38	10.576%	$165.1784	$165.18	$165.20	$165.20
Purchase #3	$28.37	3.123%	$29.256	$29.26	$29.25	$29.30
Purchase #4	$141.90	7.441%	$152.4588	$152.46	$152.45	$152.50
Purchase #5	$240.28	11.836%	$268.7195	$268.72	$268.70	$268.70
Purchase #6	$224.57	12.872%	$253.4767	$253.48	$253.50	$253.50
Purchase #7	$72.46	13.650%	$82.3508	$82.35	$82.35	$82.40
7 purchase totals =	$983.28		$1,088.3256	$1,088.34	$1,088.35	$1,088.50