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	$27.94	11.294%	$31.0955	$31.10	$31.10	$31.10
Purchase #2	$83.79	6.603%	$89.3227	$89.32	$89.30	$89.30
Purchase #3	$99.62	9.511%	$109.0949	$109.09	$109.10	$109.10
Purchase #4	$87.90	7.518%	$94.5083	$94.51	$94.50	$94.50
Purchase #5	$114.68	9.646%	$125.742	$125.74	$125.75	$125.70
Purchase #6	$235.70	8.113%	$254.8223	$254.82	$254.80	$254.80
Purchase #7	$225.26	10.675%	$249.3065	$249.31	$249.30	$249.30
7 purchase totals =	$874.89		$953.8922	$953.89	$953.85	$953.80