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	$22.57	12.360%	$25.3597	$25.36	$25.35	$25.40
Purchase #2	$37.70	6.579%	$40.1803	$40.18	$40.20	$40.20
Purchase #3	$226.29	9.289%	$247.3101	$247.31	$247.30	$247.30
Purchase #4	$245.98	3.377%	$254.2867	$254.29	$254.30	$254.30
Purchase #5	$85.59	7.871%	$92.3268	$92.33	$92.35	$92.30
Purchase #6	$223.33	12.124%	$250.4065	$250.41	$250.40	$250.40
Purchase #7	$82.27	10.277%	$90.7249	$90.72	$90.70	$90.70
7 purchase totals =	$923.73		$1,000.5950	$1,000.60	$1,000.60	$1,000.60