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	$223.66	11.872%	$250.2129	$250.21	$250.20	$250.20
Purchase #2	$61.90	3.262%	$63.9192	$63.92	$63.90	$63.90
Purchase #3	$119.30	7.468%	$128.2093	$128.21	$128.20	$128.20
Purchase #4	$125.52	11.448%	$139.8895	$139.89	$139.90	$139.90
Purchase #5	$96.65	13.349%	$109.5518	$109.55	$109.55	$109.60
Purchase #6	$79.85	12.288%	$89.662	$89.66	$89.65	$89.70
Purchase #7	$31.73	12.795%	$35.7899	$35.79	$35.80	$35.80
7 purchase totals =	$738.61		$817.2346	$817.23	$817.20	$817.30