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	$186.50	7.143%	$199.8217	$199.82	$199.80	$199.80
Purchase #2	$168.44	7.331%	$180.7883	$180.79	$180.80	$180.80
Purchase #3	$240.51	11.319%	$267.7333	$267.73	$267.75	$267.70
Purchase #4	$5.89	9.165%	$6.4298	$6.43	$6.45	$6.40
Purchase #5	$116.60	12.352%	$131.0024	$131.00	$131.00	$131.00
Purchase #6	$33.61	12.229%	$37.7202	$37.72	$37.70	$37.70
Purchase #7	$202.61	12.218%	$227.3649	$227.36	$227.35	$227.40
7 purchase totals =	$954.16		$1,050.8606	$1,050.85	$1,050.85	$1,050.80