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	$64.63	8.398%	$70.0576	$70.06	$70.05	$70.10
Purchase #2	$142.73	9.336%	$156.0553	$156.06	$156.05	$156.10
Purchase #3	$62.59	8.428%	$67.8651	$67.87	$67.85	$67.90
Purchase #4	$113.46	10.713%	$125.615	$125.62	$125.60	$125.60
Purchase #5	$56.31	9.754%	$61.8025	$61.80	$61.80	$61.80
Purchase #6	$215.35	13.262%	$243.9097	$243.91	$243.90	$243.90
Purchase #7	$172.82	5.591%	$182.4824	$182.48	$182.50	$182.50
7 purchase totals =	$827.89		$907.7876	$907.80	$907.75	$907.90