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	$25.86	7.646%	$27.8373	$27.84	$27.85	$27.80
Purchase #2	$201.91	3.700%	$209.3807	$209.38	$209.40	$209.40
Purchase #3	$192.72	11.727%	$215.3203	$215.32	$215.30	$215.30
Purchase #4	$119.33	7.169%	$127.8848	$127.88	$127.90	$127.90
Purchase #5	$191.60	9.817%	$210.4094	$210.41	$210.40	$210.40
Purchase #6	$188.30	5.315%	$198.3081	$198.31	$198.30	$198.30
Purchase #7	$28.35	7.798%	$30.5607	$30.56	$30.55	$30.60
7 purchase totals =	$948.07		$1,019.7013	$1,019.70	$1,019.70	$1,019.70