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	$167.89	12.800%	$189.3799	$189.38	$189.40	$189.40
Purchase #2	$243.54	6.402%	$259.1314	$259.13	$259.15	$259.10
Purchase #3	$192.36	12.816%	$217.0129	$217.01	$217.00	$217.00
Purchase #4	$30.83	8.786%	$33.5387	$33.54	$33.55	$33.50
Purchase #5	$84.53	5.837%	$89.464	$89.46	$89.45	$89.50
Purchase #6	$123.48	3.494%	$127.7944	$127.79	$127.80	$127.80
Purchase #7	$92.39	12.459%	$103.9009	$103.90	$103.90	$103.90
7 purchase totals =	$935.02		$1,020.2222	$1,020.21	$1,020.25	$1,020.20