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	$36.45	5.410%	$38.4219	$38.42	$38.40	$38.40
Purchase #2	$41.48	8.165%	$44.8668	$44.87	$44.85	$44.90
Purchase #3	$226.61	3.220%	$233.9068	$233.91	$233.90	$233.90
Purchase #4	$73.40	12.331%	$82.451	$82.45	$82.45	$82.50
Purchase #5	$206.40	4.850%	$216.4104	$216.41	$216.40	$216.40
Purchase #6	$137.34	10.560%	$151.8431	$151.84	$151.85	$151.80
Purchase #7	$200.54	12.708%	$226.0246	$226.02	$226.00	$226.00
7 purchase totals =	$922.22		$993.9246	$993.92	$993.85	$993.90