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	$47.67	11.863%	$53.3251	$53.33	$53.35	$53.30
Purchase #2	$177.62	10.513%	$196.2932	$196.29	$196.30	$196.30
Purchase #3	$212.89	6.404%	$226.5235	$226.52	$226.50	$226.50
Purchase #4	$28.87	10.265%	$31.8335	$31.83	$31.85	$31.80
Purchase #5	$209.34	3.136%	$215.9049	$215.90	$215.90	$215.90
Purchase #6	$56.34	4.776%	$59.0308	$59.03	$59.05	$59.00
Purchase #7	$14.69	9.207%	$16.0425	$16.04	$16.05	$16.00
7 purchase totals =	$747.42		$798.9535	$798.94	$799.00	$798.80