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	$61.44	4.654%	$64.2994	$64.30	$64.30	$64.30
Purchase #2	$202.94	3.435%	$209.911	$209.91	$209.90	$209.90
Purchase #3	$119.86	9.693%	$131.478	$131.48	$131.50	$131.50
Purchase #4	$142.44	11.347%	$158.6027	$158.60	$158.60	$158.60
Purchase #5	$6.78	9.253%	$7.4074	$7.41	$7.40	$7.40
Purchase #6	$63.26	13.522%	$71.814	$71.81	$71.80	$71.80
Purchase #7	$21.56	3.561%	$22.3278	$22.33	$22.35	$22.30
7 purchase totals =	$618.28		$665.8403	$665.84	$665.85	$665.80