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	$109.89	5.454%	$115.8834	$115.88	$115.90	$115.90
Purchase #2	$90.46	9.616%	$99.1586	$99.16	$99.15	$99.20
Purchase #3	$84.40	8.711%	$91.7521	$91.75	$91.75	$91.80
Purchase #4	$65.88	8.447%	$71.4449	$71.44	$71.45	$71.40
Purchase #5	$191.68	11.393%	$213.5181	$213.52	$213.50	$213.50
Purchase #6	$233.53	4.386%	$243.7726	$243.77	$243.75	$243.80
Purchase #7	$124.78	13.709%	$141.8861	$141.89	$141.90	$141.90
7 purchase totals =	$900.62		$977.4158	$977.41	$977.40	$977.50