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	$7.76	8.850%	$8.4468	$8.45	$8.45	$8.40
Purchase #2	$211.38	9.703%	$231.8902	$231.89	$231.90	$231.90
Purchase #3	$242.75	13.250%	$274.9144	$274.91	$274.90	$274.90
Purchase #4	$75.39	9.521%	$82.5679	$82.57	$82.55	$82.60
Purchase #5	$83.74	7.168%	$89.7425	$89.74	$89.75	$89.70
Purchase #6	$214.83	8.420%	$232.9187	$232.92	$232.90	$232.90
Purchase #7	$85.34	7.534%	$91.7695	$91.77	$91.75	$91.80
7 purchase totals =	$921.19		$1,012.2500	$1,012.25	$1,012.20	$1,012.20