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	$248.54	6.297%	$264.1906	$264.19	$264.20	$264.20
Purchase #2	$67.43	5.227%	$70.9546	$70.95	$70.95	$71.00
Purchase #3	$10.65	12.516%	$11.983	$11.98	$12.00	$12.00
Purchase #4	$140.90	3.765%	$146.2049	$146.20	$146.20	$146.20
Purchase #5	$248.31	10.690%	$274.8543	$274.85	$274.85	$274.90
Purchase #6	$160.45	11.870%	$179.4954	$179.50	$179.50	$179.50
Purchase #7	$50.33	11.466%	$56.1008	$56.10	$56.10	$56.10
7 purchase totals =	$926.61		$1,003.7836	$1,003.77	$1,003.80	$1,003.90