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	$201.48	3.600%	$208.7333	$208.73	$208.75	$208.70
Purchase #2	$32.65	8.354%	$35.3776	$35.38	$35.40	$35.40
Purchase #3	$120.61	6.183%	$128.0673	$128.07	$128.05	$128.10
Purchase #4	$158.76	13.391%	$180.0196	$180.02	$180.00	$180.00
Purchase #5	$24.94	13.751%	$28.3695	$28.37	$28.35	$28.40
Purchase #6	$89.96	10.380%	$99.2978	$99.30	$99.30	$99.30
Purchase #7	$80.46	10.698%	$89.0676	$89.07	$89.05	$89.10
7 purchase totals =	$708.86		$768.9327	$768.94	$768.90	$769.00