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	$84.42	6.638%	$90.0238	$90.02	$90.00	$90.00
Purchase #2	$231.53	10.238%	$255.234	$255.23	$255.25	$255.20
Purchase #3	$96.27	8.614%	$104.5627	$104.56	$104.55	$104.60
Purchase #4	$43.61	9.279%	$47.6566	$47.66	$47.65	$47.70
Purchase #5	$170.89	8.480%	$185.3815	$185.38	$185.40	$185.40
Purchase #6	$71.92	8.490%	$78.026	$78.03	$78.05	$78.00
Purchase #7	$157.38	12.773%	$177.4821	$177.48	$177.50	$177.50
7 purchase totals =	$856.02		$938.3667	$938.36	$938.40	$938.40