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	$113.95	12.590%	$128.2963	$128.30	$128.30	$128.30
Purchase #2	$146.75	6.107%	$155.712	$155.71	$155.70	$155.70
Purchase #3	$68.35	5.232%	$71.9261	$71.93	$71.95	$71.90
Purchase #4	$154.91	3.547%	$160.4047	$160.40	$160.40	$160.40
Purchase #5	$120.85	13.445%	$137.0983	$137.10	$137.10	$137.10
Purchase #6	$180.33	5.333%	$189.947	$189.95	$189.95	$189.90
Purchase #7	$150.75	6.515%	$160.5714	$160.57	$160.55	$160.60
7 purchase totals =	$935.89		$1,003.9558	$1,003.96	$1,003.95	$1,003.90