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	$236.69	5.428%	$249.5375	$249.54	$249.55	$249.50
Purchase #2	$150.98	11.465%	$168.2899	$168.29	$168.30	$168.30
Purchase #3	$185.76	12.726%	$209.3998	$209.40	$209.40	$209.40
Purchase #4	$22.67	8.209%	$24.531	$24.53	$24.55	$24.50
Purchase #5	$55.85	9.363%	$61.0792	$61.08	$61.10	$61.10
Purchase #6	$111.85	11.515%	$124.7295	$124.73	$124.75	$124.70
Purchase #7	$186.71	5.215%	$196.4469	$196.45	$196.45	$196.40
7 purchase totals =	$950.51		$1,034.0138	$1,034.02	$1,034.10	$1,033.90