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	$26.69	7.782%	$28.767	$28.77	$28.75	$28.80
Purchase #2	$222.96	4.843%	$233.758	$233.76	$233.75	$233.80
Purchase #3	$14.99	12.607%	$16.8798	$16.88	$16.90	$16.90
Purchase #4	$82.78	3.761%	$85.8934	$85.89	$85.90	$85.90
Purchase #5	$69.57	4.518%	$72.7132	$72.71	$72.70	$72.70
Purchase #6	$39.64	11.838%	$44.3326	$44.33	$44.35	$44.30
Purchase #7	$51.90	7.106%	$55.588	$55.59	$55.60	$55.60
7 purchase totals =	$508.53		$537.9320	$537.93	$537.95	$538.00