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	$101.40	5.220%	$106.6931	$106.69	$106.70	$106.70
Purchase #2	$84.29	5.607%	$89.0161	$89.02	$89.00	$89.00
Purchase #3	$135.55	6.686%	$144.6129	$144.61	$144.60	$144.60
Purchase #4	$20.61	12.869%	$23.2623	$23.26	$23.25	$23.30
Purchase #5	$203.76	6.443%	$216.8883	$216.89	$216.90	$216.90
Purchase #6	$140.52	7.507%	$151.0688	$151.07	$151.05	$151.10
Purchase #7	$220.29	12.266%	$247.3108	$247.31	$247.30	$247.30
7 purchase totals =	$906.42		$978.8523	$978.85	$978.80	$978.90