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	$98.96	6.385%	$105.2786	$105.28	$105.30	$105.30
Purchase #2	$25.70	10.588%	$28.4211	$28.42	$28.40	$28.40
Purchase #3	$88.57	5.586%	$93.5175	$93.52	$93.50	$93.50
Purchase #4	$103.90	9.507%	$113.7778	$113.78	$113.80	$113.80
Purchase #5	$106.27	11.527%	$118.5197	$118.52	$118.50	$118.50
Purchase #6	$201.46	10.641%	$222.8974	$222.90	$222.90	$222.90
Purchase #7	$125.86	11.421%	$140.2345	$140.23	$140.25	$140.20
7 purchase totals =	$750.72		$822.6466	$822.65	$822.65	$822.60