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	$28.79	10.253%	$31.7418	$31.74	$31.75	$31.70
Purchase #2	$69.66	12.489%	$78.3598	$78.36	$78.35	$78.40
Purchase #3	$73.72	6.662%	$78.6312	$78.63	$78.65	$78.60
Purchase #4	$130.25	9.574%	$142.7201	$142.72	$142.70	$142.70
Purchase #5	$156.95	5.643%	$165.8067	$165.81	$165.80	$165.80
Purchase #6	$168.77	12.432%	$189.7515	$189.75	$189.75	$189.80
Purchase #7	$64.74	11.142%	$71.9533	$71.95	$71.95	$72.00
7 purchase totals =	$692.88		$758.9644	$758.96	$758.95	$759.00