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	$98.82	6.664%	$105.4054	$105.41	$105.40	$105.40
Purchase #2	$250.55	3.591%	$259.5473	$259.55	$259.55	$259.50
Purchase #3	$241.98	11.721%	$270.3425	$270.34	$270.35	$270.30
Purchase #4	$162.34	5.590%	$171.4148	$171.41	$171.40	$171.40
Purchase #5	$76.60	8.404%	$83.0375	$83.04	$83.05	$83.00
Purchase #6	$96.40	13.496%	$109.4101	$109.41	$109.40	$109.40
Purchase #7	$249.86	10.754%	$276.7299	$276.73	$276.75	$276.70
7 purchase totals =	$1,176.55		$1,275.8875	$1,275.89	$1,275.90	$1,275.70