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	$39.29	7.493%	$42.234	$42.23	$42.25	$42.20
Purchase #2	$200.57	13.356%	$227.3581	$227.36	$227.35	$227.40
Purchase #3	$100.73	8.654%	$109.4472	$109.45	$109.45	$109.40
Purchase #4	$29.79	6.466%	$31.7162	$31.72	$31.70	$31.70
Purchase #5	$242.94	12.809%	$274.0582	$274.06	$274.05	$274.10
Purchase #6	$169.36	13.275%	$191.8425	$191.84	$191.85	$191.80
Purchase #7	$202.66	6.366%	$215.5613	$215.56	$215.55	$215.60
7 purchase totals =	$985.34		$1,092.2175	$1,092.22	$1,092.20	$1,092.20