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	$178.97	12.256%	$200.9046	$200.90	$200.90	$200.90
Purchase #2	$150.56	7.809%	$162.3172	$162.32	$162.30	$162.30
Purchase #3	$59.50	13.501%	$67.5331	$67.53	$67.55	$67.50
Purchase #4	$33.82	10.298%	$37.3028	$37.30	$37.30	$37.30
Purchase #5	$211.93	12.503%	$238.4276	$238.43	$238.45	$238.40
Purchase #6	$248.33	10.207%	$273.677	$273.68	$273.70	$273.70
Purchase #7	$74.55	3.186%	$76.9252	$76.93	$76.95	$76.90
7 purchase totals =	$957.66		$1,057.0875	$1,057.09	$1,057.15	$1,057.00