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	$164.34	13.792%	$187.0058	$187.01	$187.00	$187.00
Purchase #2	$36.32	3.361%	$37.5407	$37.54	$37.55	$37.50
Purchase #3	$200.37	13.558%	$227.5362	$227.54	$227.55	$227.50
Purchase #4	$242.50	12.129%	$271.9128	$271.91	$271.90	$271.90
Purchase #5	$89.47	10.538%	$98.8983	$98.90	$98.90	$98.90
Purchase #6	$207.59	12.287%	$233.0966	$233.10	$233.10	$233.10
Purchase #7	$215.40	5.870%	$228.044	$228.04	$228.05	$228.00
7 purchase totals =	$1,155.99		$1,284.0344	$1,284.04	$1,284.05	$1,283.90