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	$25.99	9.303%	$28.4078	$28.41	$28.40	$28.40
Purchase #2	$234.38	12.797%	$264.3736	$264.37	$264.35	$264.40
Purchase #3	$36.97	11.463%	$41.2079	$41.21	$41.20	$41.20
Purchase #4	$244.99	4.596%	$256.2497	$256.25	$256.25	$256.20
Purchase #5	$34.74	10.312%	$38.3224	$38.32	$38.30	$38.30
Purchase #6	$86.25	11.684%	$96.3275	$96.33	$96.35	$96.30
Purchase #7	$53.88	10.401%	$59.4841	$59.48	$59.50	$59.50
7 purchase totals =	$717.20		$784.3730	$784.37	$784.35	$784.30