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	$28.85	10.206%	$31.7944	$31.79	$31.80	$31.80
Purchase #2	$101.90	7.292%	$109.3305	$109.33	$109.35	$109.30
Purchase #3	$183.41	6.227%	$194.8309	$194.83	$194.85	$194.80
Purchase #4	$72.90	7.367%	$78.2705	$78.27	$78.25	$78.30
Purchase #5	$101.95	10.140%	$112.2877	$112.29	$112.30	$112.30
Purchase #6	$142.68	5.271%	$150.2007	$150.20	$150.20	$150.20
Purchase #7	$242.62	10.433%	$267.9325	$267.93	$267.95	$267.90
7 purchase totals =	$874.31		$944.6472	$944.64	$944.70	$944.60