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	$7.54	3.192%	$7.7807	$7.78	$7.80	$7.80
Purchase #2	$56.73	5.154%	$59.6539	$59.65	$59.65	$59.70
Purchase #3	$207.31	4.865%	$217.3956	$217.40	$217.40	$217.40
Purchase #4	$200.92	4.391%	$209.7424	$209.74	$209.75	$209.70
Purchase #5	$210.53	7.102%	$225.4818	$225.48	$225.50	$225.50
Purchase #6	$201.86	11.351%	$224.7731	$224.77	$224.75	$224.80
Purchase #7	$149.37	10.363%	$164.8492	$164.85	$164.85	$164.80
7 purchase totals =	$1,034.26		$1,109.6767	$1,109.67	$1,109.70	$1,109.70