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	$120.57	3.270%	$124.5126	$124.51	$124.50	$124.50
Purchase #2	$184.25	7.791%	$198.6049	$198.60	$198.60	$198.60
Purchase #3	$168.37	4.334%	$175.6672	$175.67	$175.65	$175.70
Purchase #4	$102.52	8.832%	$111.5746	$111.57	$111.55	$111.60
Purchase #5	$67.34	12.216%	$75.5663	$75.57	$75.55	$75.60
Purchase #6	$227.76	5.738%	$240.8289	$240.83	$240.85	$240.80
Purchase #7	$32.33	3.678%	$33.5191	$33.52	$33.50	$33.50
7 purchase totals =	$903.14		$960.2736	$960.27	$960.20	$960.30