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	$83.31	7.340%	$89.425	$89.43	$89.45	$89.40
Purchase #2	$245.46	11.436%	$273.5308	$273.53	$273.55	$273.50
Purchase #3	$175.48	6.798%	$187.4091	$187.41	$187.40	$187.40
Purchase #4	$189.78	12.226%	$212.9825	$212.98	$213.00	$213.00
Purchase #5	$188.80	12.190%	$211.8147	$211.81	$211.80	$211.80
Purchase #6	$189.61	5.659%	$200.34	$200.34	$200.35	$200.30
Purchase #7	$203.45	7.236%	$218.1716	$218.17	$218.15	$218.20
7 purchase totals =	$1,275.89		$1,393.6737	$1,393.67	$1,393.70	$1,393.60