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	$76.34	5.264%	$80.3585	$80.36	$80.35	$80.40
Purchase #2	$202.90	13.144%	$229.5692	$229.57	$229.55	$229.60
Purchase #3	$134.25	11.102%	$149.1544	$149.15	$149.15	$149.20
Purchase #4	$121.69	5.583%	$128.484	$128.48	$128.50	$128.50
Purchase #5	$94.89	5.179%	$99.8044	$99.80	$99.80	$99.80
Purchase #6	$74.38	5.420%	$78.4114	$78.41	$78.40	$78.40
Purchase #7	$77.33	11.526%	$86.2431	$86.24	$86.25	$86.20
7 purchase totals =	$781.78		$852.0250	$852.01	$852.00	$852.10