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	$151.65	13.361%	$171.912	$171.91	$171.90	$171.90
Purchase #2	$206.44	3.423%	$213.5064	$213.51	$213.50	$213.50
Purchase #3	$215.43	3.280%	$222.4961	$222.50	$222.50	$222.50
Purchase #4	$128.98	9.217%	$140.8681	$140.87	$140.85	$140.90
Purchase #5	$209.70	8.614%	$227.7636	$227.76	$227.75	$227.80
Purchase #6	$142.74	8.841%	$155.3596	$155.36	$155.35	$155.40
Purchase #7	$237.66	13.835%	$270.5403	$270.54	$270.55	$270.50
7 purchase totals =	$1,292.60		$1,402.4461	$1,402.45	$1,402.40	$1,402.50