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	$113.93	12.760%	$128.4675	$128.47	$128.45	$128.50
Purchase #2	$171.53	11.690%	$191.5819	$191.58	$191.60	$191.60
Purchase #3	$104.85	7.250%	$112.4516	$112.45	$112.45	$112.50
Purchase #4	$209.36	9.817%	$229.9129	$229.91	$229.90	$229.90
Purchase #5	$38.73	9.264%	$42.3179	$42.32	$42.30	$42.30
Purchase #6	$238.35	8.751%	$259.208	$259.21	$259.20	$259.20
Purchase #7	$220.45	11.355%	$245.4821	$245.48	$245.50	$245.50
7 purchase totals =	$1,097.20		$1,209.4219	$1,209.42	$1,209.40	$1,209.50