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	$71.68	9.542%	$78.5197	$78.52	$78.50	$78.50
Purchase #2	$36.67	12.379%	$41.2094	$41.21	$41.20	$41.20
Purchase #3	$84.70	8.398%	$91.8131	$91.81	$91.80	$91.80
Purchase #4	$129.33	4.257%	$134.8356	$134.84	$134.85	$134.80
Purchase #5	$32.40	3.467%	$33.5233	$33.52	$33.50	$33.50
Purchase #6	$93.65	10.474%	$103.4589	$103.46	$103.45	$103.50
Purchase #7	$200.89	7.645%	$216.248	$216.25	$216.25	$216.20
7 purchase totals =	$649.32		$699.6080	$699.61	$699.55	$699.50