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	$164.32	12.321%	$184.5659	$184.57	$184.55	$184.60
Purchase #2	$42.38	5.753%	$44.8181	$44.82	$44.80	$44.80
Purchase #3	$189.67	12.597%	$213.5627	$213.56	$213.55	$213.60
Purchase #4	$206.67	3.813%	$214.5503	$214.55	$214.55	$214.60
Purchase #5	$80.92	12.165%	$90.7639	$90.76	$90.75	$90.80
Purchase #6	$82.89	10.651%	$91.7186	$91.72	$91.70	$91.70
Purchase #7	$148.32	5.800%	$156.9226	$156.92	$156.90	$156.90
7 purchase totals =	$915.17		$996.9021	$996.90	$996.80	$997.00