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	$33.87	10.843%	$37.5425	$37.54	$37.55	$37.50
Purchase #2	$119.86	8.740%	$130.3358	$130.34	$130.35	$130.30
Purchase #3	$31.45	6.706%	$33.559	$33.56	$33.55	$33.60
Purchase #4	$249.87	12.275%	$280.5415	$280.54	$280.55	$280.50
Purchase #5	$217.64	6.755%	$232.3416	$232.34	$232.35	$232.30
Purchase #6	$78.73	11.556%	$87.828	$87.83	$87.85	$87.80
Purchase #7	$52.94	5.689%	$55.9518	$55.95	$55.95	$56.00
7 purchase totals =	$784.36		$858.1002	$858.10	$858.15	$858.00