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	$81.77	11.107%	$90.8522	$90.85	$90.85	$90.90
Purchase #2	$202.56	7.539%	$217.831	$217.83	$217.85	$217.80
Purchase #3	$190.90	4.779%	$200.0231	$200.02	$200.00	$200.00
Purchase #4	$96.73	3.271%	$99.894	$99.89	$99.90	$99.90
Purchase #5	$5.79	9.845%	$6.36	$6.36	$6.35	$6.40
Purchase #6	$223.56	11.629%	$249.5578	$249.56	$249.55	$249.60
Purchase #7	$56.71	3.264%	$58.561	$58.56	$58.55	$58.60
7 purchase totals =	$858.02		$923.0791	$923.07	$923.05	$923.20