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	$186.55	6.764%	$199.1682	$199.17	$199.15	$199.20
Purchase #2	$123.48	13.511%	$140.1634	$140.16	$140.15	$140.20
Purchase #3	$162.96	11.278%	$181.3386	$181.34	$181.35	$181.30
Purchase #4	$124.88	5.650%	$131.9357	$131.94	$131.95	$131.90
Purchase #5	$27.67	7.539%	$29.756	$29.76	$29.75	$29.80
Purchase #6	$243.48	11.129%	$270.5769	$270.58	$270.60	$270.60
Purchase #7	$191.33	12.449%	$215.1487	$215.15	$215.15	$215.10
7 purchase totals =	$1,060.35		$1,168.0875	$1,168.10	$1,168.10	$1,168.10