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	$124.41	12.625%	$140.1168	$140.12	$140.10	$140.10
Purchase #2	$185.46	9.587%	$203.2401	$203.24	$203.25	$203.20
Purchase #3	$33.46	11.535%	$37.3196	$37.32	$37.30	$37.30
Purchase #4	$29.71	4.543%	$31.0597	$31.06	$31.05	$31.10
Purchase #5	$89.66	10.598%	$99.1622	$99.16	$99.15	$99.20
Purchase #6	$11.78	12.680%	$13.2737	$13.27	$13.25	$13.30
Purchase #7	$81.81	5.865%	$86.6082	$86.61	$86.60	$86.60
7 purchase totals =	$556.29		$610.7803	$610.78	$610.70	$610.80