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	$45.37	13.419%	$51.4582	$51.46	$51.45	$51.50
Purchase #2	$89.88	9.407%	$98.335	$98.34	$98.35	$98.30
Purchase #3	$77.89	11.539%	$86.8777	$86.88	$86.90	$86.90
Purchase #4	$96.27	5.290%	$101.3627	$101.36	$101.35	$101.40
Purchase #5	$171.75	11.324%	$191.199	$191.20	$191.20	$191.20
Purchase #6	$122.32	13.198%	$138.4638	$138.46	$138.45	$138.50
Purchase #7	$113.90	3.136%	$117.4719	$117.47	$117.45	$117.50
7 purchase totals =	$717.38		$785.1683	$785.17	$785.15	$785.30