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	$88.96	12.210%	$99.822	$99.82	$99.80	$99.80
Purchase #2	$231.99	12.609%	$261.2416	$261.24	$261.25	$261.20
Purchase #3	$27.80	12.769%	$31.3498	$31.35	$31.35	$31.30
Purchase #4	$223.29	8.516%	$242.3054	$242.31	$242.30	$242.30
Purchase #5	$237.76	3.400%	$245.8438	$245.84	$245.85	$245.80
Purchase #6	$212.61	3.391%	$219.8196	$219.82	$219.80	$219.80
Purchase #7	$38.50	9.171%	$42.0308	$42.03	$42.05	$42.00
7 purchase totals =	$1,060.91		$1,142.4130	$1,142.41	$1,142.40	$1,142.20