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	$54.29	6.586%	$57.8655	$57.87	$57.85	$57.90
Purchase #2	$84.28	6.604%	$89.8459	$89.85	$89.85	$89.80
Purchase #3	$229.88	11.507%	$256.3323	$256.33	$256.35	$256.30
Purchase #4	$83.32	9.714%	$91.4137	$91.41	$91.40	$91.40
Purchase #5	$86.36	11.201%	$96.0332	$96.03	$96.05	$96.00
Purchase #6	$36.28	4.659%	$37.9703	$37.97	$37.95	$38.00
Purchase #7	$59.68	7.595%	$64.2127	$64.21	$64.20	$64.20
7 purchase totals =	$634.09		$693.6736	$693.67	$693.65	$693.60