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	$90.69	9.868%	$99.6393	$99.64	$99.65	$99.60
Purchase #2	$247.89	10.345%	$273.5342	$273.53	$273.55	$273.50
Purchase #3	$150.92	12.342%	$169.5465	$169.55	$169.55	$169.50
Purchase #4	$197.56	9.222%	$215.779	$215.78	$215.80	$215.80
Purchase #5	$69.36	8.835%	$75.488	$75.49	$75.50	$75.50
Purchase #6	$100.87	5.602%	$106.5207	$106.52	$106.50	$106.50
Purchase #7	$63.55	12.718%	$71.6323	$71.63	$71.65	$71.60
7 purchase totals =	$920.84		$1,012.1400	$1,012.14	$1,012.20	$1,012.00