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	$172.51	9.228%	$188.4292	$188.43	$188.45	$188.40
Purchase #2	$203.97	3.640%	$211.3945	$211.39	$211.40	$211.40
Purchase #3	$160.98	11.754%	$179.9016	$179.90	$179.90	$179.90
Purchase #4	$145.97	10.663%	$161.5348	$161.53	$161.55	$161.50
Purchase #5	$134.59	3.524%	$139.333	$139.33	$139.35	$139.30
Purchase #6	$40.44	12.285%	$45.4081	$45.41	$45.40	$45.40
Purchase #7	$65.39	9.152%	$71.3745	$71.37	$71.35	$71.40
7 purchase totals =	$923.85		$997.3757	$997.36	$997.40	$997.30