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	$25.30	13.222%	$28.6452	$28.65	$28.65	$28.60
Purchase #2	$102.86	10.661%	$113.8259	$113.83	$113.85	$113.80
Purchase #3	$100.26	9.221%	$109.505	$109.51	$109.50	$109.50
Purchase #4	$162.48	3.310%	$167.8581	$167.86	$167.85	$167.90
Purchase #5	$131.97	12.143%	$147.9951	$148.00	$148.00	$148.00
Purchase #6	$140.62	4.618%	$147.1138	$147.11	$147.10	$147.10
Purchase #7	$78.33	10.274%	$86.3776	$86.38	$86.40	$86.40
7 purchase totals =	$741.82		$801.3207	$801.34	$801.35	$801.30