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	$47.81	4.357%	$49.8931	$49.89	$49.90	$49.90
Purchase #2	$88.48	13.496%	$100.4213	$100.42	$100.40	$100.40
Purchase #3	$178.62	12.792%	$201.4691	$201.47	$201.45	$201.50
Purchase #4	$5.59	4.654%	$5.8502	$5.85	$5.85	$5.90
Purchase #5	$152.42	12.764%	$171.8749	$171.87	$171.85	$171.90
Purchase #6	$67.40	6.127%	$71.5296	$71.53	$71.55	$71.50
Purchase #7	$133.49	10.274%	$147.2048	$147.20	$147.20	$147.20
7 purchase totals =	$673.81		$748.2430	$748.23	$748.20	$748.30