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	$163.77	12.570%	$184.3559	$184.36	$184.35	$184.40
Purchase #2	$93.69	6.616%	$99.8885	$99.89	$99.90	$99.90
Purchase #3	$18.41	9.723%	$20.2	$20.20	$20.20	$20.20
Purchase #4	$199.73	8.431%	$216.5692	$216.57	$216.55	$216.60
Purchase #5	$196.86	13.482%	$223.4007	$223.40	$223.40	$223.40
Purchase #6	$131.29	12.322%	$147.4676	$147.47	$147.45	$147.50
Purchase #7	$173.65	4.497%	$181.459	$181.46	$181.45	$181.50
7 purchase totals =	$977.40		$1,073.3409	$1,073.35	$1,073.30	$1,073.50