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	$129.75	6.339%	$137.9749	$137.97	$137.95	$138.00
Purchase #2	$34.96	11.547%	$38.9968	$39.00	$39.00	$39.00
Purchase #3	$28.63	13.654%	$32.5391	$32.54	$32.55	$32.50
Purchase #4	$33.81	11.653%	$37.7499	$37.75	$37.75	$37.70
Purchase #5	$83.44	7.663%	$89.834	$89.83	$89.85	$89.80
Purchase #6	$67.70	7.168%	$72.5527	$72.55	$72.55	$72.60
Purchase #7	$83.90	10.614%	$92.8051	$92.81	$92.80	$92.80
7 purchase totals =	$462.19		$502.4525	$502.45	$502.45	$502.40