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	$124.26	5.588%	$131.2036	$131.20	$131.20	$131.20
Purchase #2	$98.78	4.602%	$103.3259	$103.33	$103.35	$103.30
Purchase #3	$54.67	10.423%	$60.3683	$60.37	$60.35	$60.40
Purchase #4	$171.82	8.165%	$185.8491	$185.85	$185.85	$185.80
Purchase #5	$51.43	10.754%	$56.9608	$56.96	$56.95	$57.00
Purchase #6	$73.32	6.869%	$78.3564	$78.36	$78.35	$78.40
Purchase #7	$137.96	4.537%	$144.2192	$144.22	$144.20	$144.20
7 purchase totals =	$712.24		$760.2833	$760.29	$760.25	$760.30