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	$74.56	11.212%	$82.9197	$82.92	$82.90	$82.90
Purchase #2	$189.69	10.471%	$209.5524	$209.55	$209.55	$209.60
Purchase #3	$64.89	4.686%	$67.9307	$67.93	$67.95	$67.90
Purchase #4	$243.58	13.212%	$275.7618	$275.76	$275.75	$275.80
Purchase #5	$180.81	5.556%	$190.8558	$190.86	$190.85	$190.90
Purchase #6	$37.49	12.567%	$42.2014	$42.20	$42.20	$42.20
Purchase #7	$34.40	7.199%	$36.8765	$36.88	$36.90	$36.90
7 purchase totals =	$825.42		$906.0983	$906.10	$906.10	$906.20