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	$46.56	10.673%	$51.5293	$51.53	$51.55	$51.50
Purchase #2	$157.63	4.296%	$164.4018	$164.40	$164.40	$164.40
Purchase #3	$161.30	11.656%	$180.1011	$180.10	$180.10	$180.10
Purchase #4	$217.90	6.375%	$231.7911	$231.79	$231.80	$231.80
Purchase #5	$73.79	12.363%	$82.9127	$82.91	$82.90	$82.90
Purchase #6	$77.58	6.338%	$82.497	$82.50	$82.50	$82.50
Purchase #7	$75.38	7.360%	$80.928	$80.93	$80.95	$80.90
7 purchase totals =	$810.14		$874.1610	$874.16	$874.20	$874.10