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	$170.95	10.666%	$189.1835	$189.18	$189.20	$189.20
Purchase #2	$69.74	3.848%	$72.4236	$72.42	$72.40	$72.40
Purchase #3	$168.57	12.196%	$189.1288	$189.13	$189.15	$189.10
Purchase #4	$54.94	8.611%	$59.6709	$59.67	$59.65	$59.70
Purchase #5	$86.51	6.236%	$91.9048	$91.90	$91.90	$91.90
Purchase #6	$91.61	13.794%	$104.2467	$104.25	$104.25	$104.20
Purchase #7	$247.25	5.661%	$261.2468	$261.25	$261.25	$261.20
7 purchase totals =	$889.57		$967.8051	$967.80	$967.80	$967.70