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	$80.77	6.301%	$85.8593	$85.86	$85.85	$85.90
Purchase #2	$203.65	12.615%	$229.3404	$229.34	$229.35	$229.30
Purchase #3	$94.48	7.539%	$101.6028	$101.60	$101.60	$101.60
Purchase #4	$245.30	11.263%	$272.9281	$272.93	$272.95	$272.90
Purchase #5	$26.84	8.611%	$29.1512	$29.15	$29.15	$29.20
Purchase #6	$152.57	8.701%	$165.8451	$165.85	$165.85	$165.80
Purchase #7	$144.72	3.747%	$150.1427	$150.14	$150.15	$150.10
7 purchase totals =	$948.33		$1,034.8696	$1,034.87	$1,034.90	$1,034.80