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	$103.71	6.740%	$110.7001	$110.70	$110.70	$110.70
Purchase #2	$156.35	9.585%	$171.3361	$171.34	$171.35	$171.30
Purchase #3	$153.71	8.808%	$167.2488	$167.25	$167.25	$167.20
Purchase #4	$89.55	8.705%	$97.3453	$97.35	$97.35	$97.30
Purchase #5	$59.72	9.803%	$65.5744	$65.57	$65.55	$65.60
Purchase #6	$218.74	11.381%	$243.6348	$243.63	$243.65	$243.60
Purchase #7	$89.51	12.689%	$100.8679	$100.87	$100.85	$100.90
7 purchase totals =	$871.29		$956.7074	$956.71	$956.70	$956.60