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	$135.44	4.238%	$141.1799	$141.18	$141.20	$141.20
Purchase #2	$200.59	13.112%	$226.8914	$226.89	$226.90	$226.90
Purchase #3	$142.34	6.568%	$151.6889	$151.69	$151.70	$151.70
Purchase #4	$72.74	11.296%	$80.9567	$80.96	$80.95	$81.00
Purchase #5	$81.49	8.635%	$88.5267	$88.53	$88.55	$88.50
Purchase #6	$115.55	11.193%	$128.4835	$128.48	$128.50	$128.50
Purchase #7	$41.71	4.547%	$43.6066	$43.61	$43.60	$43.60
7 purchase totals =	$789.86		$861.3337	$861.34	$861.40	$861.40