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	$174.38	3.398%	$180.3054	$180.31	$180.30	$180.30
Purchase #2	$35.94	12.224%	$40.3333	$40.33	$40.35	$40.30
Purchase #3	$220.53	13.375%	$250.0259	$250.03	$250.05	$250.00
Purchase #4	$32.56	3.734%	$33.7758	$33.78	$33.80	$33.80
Purchase #5	$140.32	11.147%	$155.9615	$155.96	$155.95	$156.00
Purchase #6	$236.40	3.498%	$244.6693	$244.67	$244.65	$244.70
Purchase #7	$169.72	3.242%	$175.2223	$175.22	$175.20	$175.20
7 purchase totals =	$1,009.85		$1,080.2935	$1,080.30	$1,080.30	$1,080.30