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	$155.84	8.165%	$168.5643	$168.56	$168.55	$168.60
Purchase #2	$37.81	13.755%	$43.0108	$43.01	$43.00	$43.00
Purchase #3	$100.32	4.380%	$104.714	$104.71	$104.70	$104.70
Purchase #4	$80.76	10.599%	$89.3198	$89.32	$89.30	$89.30
Purchase #5	$113.48	6.405%	$120.7484	$120.75	$120.75	$120.70
Purchase #6	$37.34	10.324%	$41.195	$41.20	$41.20	$41.20
Purchase #7	$82.28	6.282%	$87.4488	$87.45	$87.45	$87.40
7 purchase totals =	$607.83		$655.0011	$655.00	$654.95	$654.90