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	$152.30	13.206%	$172.4127	$172.41	$172.40	$172.40
Purchase #2	$116.91	9.839%	$128.4128	$128.41	$128.40	$128.40
Purchase #3	$91.29	9.567%	$100.0237	$100.02	$100.00	$100.00
Purchase #4	$213.70	8.202%	$231.2277	$231.23	$231.25	$231.20
Purchase #5	$219.79	4.645%	$229.9992	$230.00	$230.00	$230.00
Purchase #6	$14.36	6.790%	$15.335	$15.34	$15.35	$15.30
Purchase #7	$202.48	3.272%	$209.1051	$209.11	$209.10	$209.10
7 purchase totals =	$1,010.83		$1,086.5162	$1,086.52	$1,086.50	$1,086.40