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	$67.90	13.480%	$77.0529	$77.05	$77.05	$77.10
Purchase #2	$196.53	11.159%	$218.4608	$218.46	$218.45	$218.50
Purchase #3	$134.84	3.665%	$139.7819	$139.78	$139.80	$139.80
Purchase #4	$40.33	12.647%	$45.4305	$45.43	$45.45	$45.40
Purchase #5	$170.37	8.319%	$184.5431	$184.54	$184.55	$184.50
Purchase #6	$32.81	11.730%	$36.6586	$36.66	$36.65	$36.70
Purchase #7	$214.96	13.472%	$243.9194	$243.92	$243.90	$243.90
7 purchase totals =	$857.74		$945.8472	$945.84	$945.85	$945.90