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	$27.32	6.850%	$29.1914	$29.19	$29.20	$29.20
Purchase #2	$57.72	3.366%	$59.6629	$59.66	$59.65	$59.70
Purchase #3	$165.52	7.132%	$177.3249	$177.32	$177.30	$177.30
Purchase #4	$92.77	9.155%	$101.2631	$101.26	$101.25	$101.30
Purchase #5	$65.41	11.436%	$72.8903	$72.89	$72.90	$72.90
Purchase #6	$64.78	10.170%	$71.3681	$71.37	$71.35	$71.40
Purchase #7	$86.34	8.586%	$93.7532	$93.75	$93.75	$93.80
7 purchase totals =	$559.86		$605.4539	$605.44	$605.40	$605.60