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	$39.42	9.869%	$43.3104	$43.31	$43.30	$43.30
Purchase #2	$98.44	11.468%	$109.7291	$109.73	$109.75	$109.70
Purchase #3	$209.76	6.471%	$223.3336	$223.33	$223.35	$223.30
Purchase #4	$190.79	11.819%	$213.3395	$213.34	$213.35	$213.30
Purchase #5	$151.66	11.466%	$169.0493	$169.05	$169.05	$169.00
Purchase #6	$148.66	13.612%	$168.8956	$168.90	$168.90	$168.90
Purchase #7	$100.87	10.595%	$111.5572	$111.56	$111.55	$111.60
7 purchase totals =	$939.60		$1,039.2147	$1,039.22	$1,039.25	$1,039.10