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	$82.84	8.295%	$89.7116	$89.71	$89.70	$89.70
Purchase #2	$247.88	3.225%	$255.8741	$255.87	$255.85	$255.90
Purchase #3	$59.91	8.191%	$64.8172	$64.82	$64.80	$64.80
Purchase #4	$234.64	9.196%	$256.2175	$256.22	$256.20	$256.20
Purchase #5	$236.48	3.112%	$243.8393	$243.84	$243.85	$243.80
Purchase #6	$19.73	12.658%	$22.2274	$22.23	$22.25	$22.20
Purchase #7	$21.73	5.228%	$22.866	$22.87	$22.85	$22.90
7 purchase totals =	$903.21		$955.5531	$955.56	$955.50	$955.50