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	$80.48	13.485%	$91.3327	$91.33	$91.35	$91.30
Purchase #2	$216.69	10.435%	$239.3016	$239.30	$239.30	$239.30
Purchase #3	$100.46	13.306%	$113.8272	$113.83	$113.85	$113.80
Purchase #4	$63.68	11.437%	$70.9631	$70.96	$70.95	$71.00
Purchase #5	$85.37	12.854%	$96.3435	$96.34	$96.35	$96.30
Purchase #6	$37.79	13.242%	$42.7942	$42.79	$42.80	$42.80
Purchase #7	$170.50	12.793%	$192.3121	$192.31	$192.30	$192.30
7 purchase totals =	$754.97		$846.8744	$846.86	$846.90	$846.80