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	$145.87	13.127%	$165.0184	$165.02	$165.00	$165.00
Purchase #2	$142.84	9.328%	$156.1641	$156.16	$156.15	$156.20
Purchase #3	$106.64	3.155%	$110.0045	$110.00	$110.00	$110.00
Purchase #4	$181.73	8.118%	$196.4828	$196.48	$196.50	$196.50
Purchase #5	$245.36	10.410%	$270.902	$270.90	$270.90	$270.90
Purchase #6	$13.35	3.487%	$13.8155	$13.82	$13.80	$13.80
Purchase #7	$45.27	10.508%	$50.027	$50.03	$50.05	$50.00
7 purchase totals =	$881.06		$962.4143	$962.41	$962.40	$962.40