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	$247.89	8.843%	$269.8109	$269.81	$269.80	$269.80
Purchase #2	$18.42	11.216%	$20.486	$20.49	$20.50	$20.50
Purchase #3	$121.48	7.722%	$130.8607	$130.86	$130.85	$130.90
Purchase #4	$41.34	13.145%	$46.7741	$46.77	$46.75	$46.80
Purchase #5	$73.78	12.199%	$82.7804	$82.78	$82.80	$82.80
Purchase #6	$152.64	9.412%	$167.0065	$167.01	$167.00	$167.00
Purchase #7	$122.26	13.847%	$139.1893	$139.19	$139.20	$139.20
7 purchase totals =	$777.81		$856.9079	$856.91	$856.90	$857.00