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	$250.48	12.270%	$281.2139	$281.21	$281.20	$281.20
Purchase #2	$170.76	6.797%	$182.3666	$182.37	$182.35	$182.40
Purchase #3	$34.63	8.239%	$37.4832	$37.48	$37.50	$37.50
Purchase #4	$109.83	8.107%	$118.7339	$118.73	$118.75	$118.70
Purchase #5	$184.43	13.391%	$209.127	$209.13	$209.15	$209.10
Purchase #6	$191.49	3.861%	$198.8834	$198.88	$198.90	$198.90
Purchase #7	$84.88	6.160%	$90.1086	$90.11	$90.10	$90.10
7 purchase totals =	$1,026.50		$1,117.9166	$1,117.91	$1,117.95	$1,117.90