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	$231.35	11.854%	$258.7742	$258.77	$258.75	$258.80
Purchase #2	$216.91	3.199%	$223.849	$223.85	$223.85	$223.80
Purchase #3	$155.48	10.457%	$171.7385	$171.74	$171.75	$171.70
Purchase #4	$40.89	5.181%	$43.0085	$43.01	$43.00	$43.00
Purchase #5	$168.91	8.235%	$182.8197	$182.82	$182.80	$182.80
Purchase #6	$213.92	12.599%	$240.8718	$240.87	$240.85	$240.90
Purchase #7	$223.82	12.513%	$251.8266	$251.83	$251.85	$251.80
7 purchase totals =	$1,251.28		$1,372.8883	$1,372.89	$1,372.85	$1,372.80