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	$40.94	3.700%	$42.4548	$42.45	$42.45	$42.50
Purchase #2	$97.48	5.596%	$102.935	$102.94	$102.95	$102.90
Purchase #3	$71.93	12.300%	$80.7774	$80.78	$80.80	$80.80
Purchase #4	$245.69	9.778%	$269.7136	$269.71	$269.70	$269.70
Purchase #5	$71.92	9.216%	$78.5481	$78.55	$78.55	$78.50
Purchase #6	$28.42	11.335%	$31.6414	$31.64	$31.65	$31.60
Purchase #7	$156.45	3.165%	$161.4016	$161.40	$161.40	$161.40
7 purchase totals =	$712.83		$767.4719	$767.47	$767.50	$767.40