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	$221.37	6.763%	$236.3413	$236.34	$236.35	$236.30
Purchase #2	$74.70	4.655%	$78.1773	$78.18	$78.20	$78.20
Purchase #3	$250.33	12.475%	$281.5587	$281.56	$281.55	$281.60
Purchase #4	$98.53	4.165%	$102.6338	$102.63	$102.65	$102.60
Purchase #5	$65.91	9.862%	$72.41	$72.41	$72.40	$72.40
Purchase #6	$229.91	12.593%	$258.8626	$258.86	$258.85	$258.90
Purchase #7	$23.97	7.801%	$25.8399	$25.84	$25.85	$25.80
7 purchase totals =	$964.72		$1,055.8236	$1,055.82	$1,055.85	$1,055.80