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	$142.45	11.849%	$159.3289	$159.33	$159.35	$159.30
Purchase #2	$59.56	3.113%	$61.4141	$61.41	$61.40	$61.40
Purchase #3	$234.32	3.440%	$242.3806	$242.38	$242.40	$242.40
Purchase #4	$79.41	7.543%	$85.3999	$85.40	$85.40	$85.40
Purchase #5	$63.53	12.303%	$71.3461	$71.35	$71.35	$71.30
Purchase #6	$169.66	12.413%	$190.7199	$190.72	$190.70	$190.70
Purchase #7	$133.70	12.871%	$150.9085	$150.91	$150.90	$150.90
7 purchase totals =	$882.63		$961.4980	$961.50	$961.50	$961.40