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	$86.73	12.463%	$97.5392	$97.54	$97.55	$97.50
Purchase #2	$207.93	7.571%	$223.6724	$223.67	$223.65	$223.70
Purchase #3	$64.43	5.275%	$67.8287	$67.83	$67.85	$67.80
Purchase #4	$219.92	9.560%	$240.9444	$240.94	$240.95	$240.90
Purchase #5	$56.91	11.404%	$63.4	$63.40	$63.40	$63.40
Purchase #6	$55.56	7.168%	$59.5425	$59.54	$59.55	$59.50
Purchase #7	$132.69	5.795%	$140.3794	$140.38	$140.40	$140.40
7 purchase totals =	$824.17		$893.3066	$893.30	$893.35	$893.20