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	$27.75	11.760%	$31.0134	$31.01	$31.00	$31.00
Purchase #2	$179.63	7.297%	$192.7376	$192.74	$192.75	$192.70
Purchase #3	$46.88	8.659%	$50.9393	$50.94	$50.95	$50.90
Purchase #4	$80.83	10.594%	$89.3931	$89.39	$89.40	$89.40
Purchase #5	$240.48	12.684%	$270.9825	$270.98	$271.00	$271.00
Purchase #6	$151.89	12.665%	$171.1269	$171.13	$171.15	$171.10
Purchase #7	$196.82	6.586%	$209.7826	$209.78	$209.80	$209.80
7 purchase totals =	$924.28		$1,015.9754	$1,015.97	$1,016.05	$1,015.90