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	$126.90	9.569%	$139.0431	$139.04	$139.05	$139.00
Purchase #2	$185.71	7.851%	$200.2901	$200.29	$200.30	$200.30
Purchase #3	$59.66	4.309%	$62.2307	$62.23	$62.25	$62.20
Purchase #4	$101.81	8.220%	$110.1788	$110.18	$110.20	$110.20
Purchase #5	$23.29	9.109%	$25.4115	$25.41	$25.40	$25.40
Purchase #6	$66.25	9.452%	$72.512	$72.51	$72.50	$72.50
Purchase #7	$201.61	9.744%	$221.2549	$221.25	$221.25	$221.30
7 purchase totals =	$765.23		$830.9211	$830.91	$830.95	$830.90