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	$31.90	7.577%	$34.3171	$34.32	$34.30	$34.30
Purchase #2	$166.82	3.207%	$172.1699	$172.17	$172.15	$172.20
Purchase #3	$229.69	7.419%	$246.7307	$246.73	$246.75	$246.70
Purchase #4	$35.40	6.465%	$37.6886	$37.69	$37.70	$37.70
Purchase #5	$54.99	8.212%	$59.5058	$59.51	$59.50	$59.50
Purchase #6	$179.57	12.245%	$201.5583	$201.56	$201.55	$201.60
Purchase #7	$73.34	12.529%	$82.5288	$82.53	$82.55	$82.50
7 purchase totals =	$771.71		$834.4992	$834.51	$834.50	$834.50