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	$45.93	9.260%	$50.1831	$50.18	$50.20	$50.20
Purchase #2	$223.46	9.761%	$245.2719	$245.27	$245.25	$245.30
Purchase #3	$124.85	10.460%	$137.9093	$137.91	$137.90	$137.90
Purchase #4	$202.26	11.410%	$225.3379	$225.34	$225.35	$225.30
Purchase #5	$90.98	10.708%	$100.7221	$100.72	$100.70	$100.70
Purchase #6	$201.31	11.582%	$224.6257	$224.63	$224.65	$224.60
Purchase #7	$84.27	3.755%	$87.4343	$87.43	$87.45	$87.40
7 purchase totals =	$973.06		$1,071.4843	$1,071.48	$1,071.50	$1,071.40