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	$6.58	9.476%	$7.2035	$7.20	$7.20	$7.20
Purchase #2	$167.28	4.362%	$174.5768	$174.58	$174.60	$174.60
Purchase #3	$88.56	13.275%	$100.3163	$100.32	$100.30	$100.30
Purchase #4	$82.50	9.776%	$90.5652	$90.57	$90.55	$90.60
Purchase #5	$146.45	11.148%	$162.7762	$162.78	$162.80	$162.80
Purchase #6	$103.94	11.801%	$116.206	$116.21	$116.20	$116.20
Purchase #7	$164.94	12.799%	$186.0507	$186.05	$186.05	$186.10
7 purchase totals =	$760.25		$837.6947	$837.71	$837.70	$837.80