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	$120.66	13.255%	$136.6535	$136.65	$136.65	$136.70
Purchase #2	$77.59	6.270%	$82.4549	$82.45	$82.45	$82.50
Purchase #3	$215.71	13.569%	$244.9797	$244.98	$245.00	$245.00
Purchase #4	$40.41	6.143%	$42.8924	$42.89	$42.90	$42.90
Purchase #5	$126.96	4.402%	$132.5488	$132.55	$132.55	$132.50
Purchase #6	$185.53	8.631%	$201.5431	$201.54	$201.55	$201.50
Purchase #7	$140.97	6.809%	$150.5686	$150.57	$150.55	$150.60
7 purchase totals =	$907.83		$991.6410	$991.63	$991.65	$991.70