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	$31.85	6.446%	$33.9031	$33.90	$33.90	$33.90
Purchase #2	$99.63	8.217%	$107.8166	$107.82	$107.80	$107.80
Purchase #3	$193.78	8.232%	$209.732	$209.73	$209.75	$209.70
Purchase #4	$90.46	7.524%	$97.2662	$97.27	$97.25	$97.30
Purchase #5	$213.78	11.555%	$238.4823	$238.48	$238.50	$238.50
Purchase #6	$78.53	8.655%	$85.3268	$85.33	$85.35	$85.30
Purchase #7	$240.59	9.463%	$263.357	$263.36	$263.35	$263.40
7 purchase totals =	$948.62		$1,035.8840	$1,035.89	$1,035.90	$1,035.90